Matter and Its Properties

Particulate Nature of Matter

Everything around us is made of matter. Matter is anything that takes up space.

A rock is matter. Water is matter. Air is matter. Your pencil, your shirt, and even a drop of juice are all matter too.

Scientists have learned that all matter is made of tiny pieces. These tiny pieces are much too small to see with just our eyes.

We can think of these tiny pieces like little building bits that make up everything. Even though they are very, very small, they are there.

Big idea: All matter is made of tiny particles, and these tiny particles are always moving.

For 2nd grade, it helps to imagine particles like tiny dots. The dots are so small that we cannot see them, but they make up all solids, liquids, and gases.

What are particles?

Particles are tiny pieces of matter. Everything is made of particles.

Some particles are called atoms. Some are groups of atoms joined together, called molecules. You do not need to see them to know they are there.

Think about a sand castle. It looks like one big thing, but it is really made of many tiny grains of sand. Matter is like that too, except the pieces are much smaller than grains of sand.

Particles are always moving

The tiny particles in matter do not stay perfectly still. They are always moving.

Sometimes they move a little. Sometimes they move a lot. How they move helps us understand solids, liquids, and gases.

Particles in a solid

In a solid, the particles are packed close together.

The particles in a solid can wiggle in place, but they do not move around very much. That is why a solid keeps its shape.

A book, a toy block, and an ice cube are solids. Their particles stay close together, so these objects keep their form.

Particles in a liquid

In a liquid, the particles are still close together, but they can slide past one another.

That is why a liquid can pour and change shape to fit its cup or bottle.

Water, milk, and juice are liquids. Their particles move more freely than the particles in a solid.

Particles in a gas

In a gas, the particles are spread farther apart.

The particles move around a lot. That is why gases spread out and fill the space around them.

Air is a gas. You cannot usually see it, but it is made of moving particles.

How do we know matter has tiny particles?

We cannot see most particles, but we can see clues.

• Sugar in water: When sugar mixes into water, it seems to disappear. It does not really vanish. Its tiny particles spread through the water.
• Smell in the air: If someone peels an orange across the room, you may smell it after a little while. Tiny particles move through the air to your nose.
• Balloon with air: A balloon gets bigger when we blow air into it. That shows air takes up space because it is made of particles.

Particles and changes

Matter can change from one state to another. The particles are still there, but they move in different ways.

When ice melts into water, it is still the same matter. The particles are now able to move more freely.

When water warms up and becomes water vapor, the particles spread farther apart and move around more.

When water cools and freezes into ice, the particles get closer together and only wiggle in place.

Worked Example 1: Is air matter?

Question: We cannot see air. Is air matter?

Think: Matter takes up space. Air can fill a balloon and make it bigger.

Answer: Yes. Air is matter because it takes up space. It is made of tiny moving particles.

Worked Example 2: Why does water change shape in a cup?

Question: When water is poured into a cup, why does it take the shape of the cup?

Think: In a liquid, particles can slide past one another.

Answer: Water changes shape because it is a liquid. Its particles are close together but can move and slide, so the water fits the cup.

Worked Example 3: Why does a rock keep its shape?

Question: A rock stays the same shape when you put it on a table. Why?

Think: In a solid, particles are packed close together and only wiggle in place.

Answer: A rock keeps its shape because it is a solid. Its particles stay very close together and do not slide around like a liquid.

Worked Example 4: Why can you smell popcorn from the kitchen?

Question: Someone makes popcorn in the kitchen. After a while, you smell it in another room. Why?

Think: Gas particles move through the air.

Answer: Tiny particles from the popcorn smell move through the air. The moving particles reach your nose, so you can smell the popcorn.

Let’s remember the three states of matter

• Solid: Particles are close together and wiggle in place.
• Liquid: Particles are close together and slide past one another.
• Gas: Particles are farther apart and move all around.

Easy ways to picture particles

You can imagine particles as tiny dots.

• In a solid, the dots are packed tightly.
• In a liquid, the dots are close but can move around each other.
• In a gas, the dots are spread out.

Why this idea matters

Knowing that matter is made of tiny moving particles helps us understand many things we see every day.

• Why ice is hard
• Why water pours
• Why air fills a ball
• Why smells travel
• Why matter can change from solid to liquid to gas

Summary

All matter is made of tiny particles. These particles are too small to see, but they are always moving.

In solids, particles stay close together and only wiggle. In liquids, particles stay close together and slide past one another. In gases, particles spread farther apart and move around a lot.

Even when matter changes shape or changes state, it is still made of particles. Thinking about tiny moving particles helps us understand the world around us.

Definition and Nature of Matter

Everything around you is made of matter. The desk, the air, your water bottle, your shoes, and even your body are all matter.

In science, matter is anything that has mass and takes up space. Another word for the space something takes up is volume.

This means that if something has mass and volume, it is matter. If it does not have mass and does not take up space, it is not matter.

Let’s break that definition into parts:

• Mass means how much “stuff” is in an object.
• Volume means how much space an object takes up.

For example, a rock has mass because it is made of matter, and it has volume because it takes up space in your hand or on the ground. A balloon filled with air also has mass and volume. Even though air is hard to see, it is still matter because it has mass and fills space inside the balloon.

Why is this important?

Knowing what matter is helps us understand the world. Scientists study matter to learn about solids, liquids, and gases, how materials change, and how different objects are alike or different.

Matter can be seen or unseen

Some matter is easy to see, like books, apples, or sand. Some matter is harder to notice, like air or water vapor. But if it has mass and takes up space, it is still matter.

Air is a great example. You cannot usually see air, but you can feel it when the wind blows. You can also see its effects when it fills a tire or blows up a balloon. That shows air takes up space.

What is not matter?

Not everything is matter. Some things are real, but they are not made of matter because they do not have mass or volume.

• Light is not matter.
• Sound is not matter.
• Heat is not matter.
• A shadow is not matter.

For example, sunlight can warm your skin, but light does not take up space the way a chair or a cup of water does. Sound can be loud or soft, but it is not a substance you can hold or pour.

Matter is made of tiny particles

All matter is made of very tiny pieces called particles. These particles are too small to see without special tools. Even though we cannot see them, they make up everything that is matter.

You can think of matter as being built from tiny pieces, the way a wall is built from bricks. The particles are very small, but together they form the objects and materials we see every day.

The three common states of matter

Matter is usually grouped into three common states:

• Solid – has its own shape and takes up space. Example: a pencil.
• Liquid – takes the shape of its container but still takes up space. Example: juice.
• Gas – spreads out to fill the space around it. Example: air.

All three states are matter because they all have mass and volume.

How can we tell if something is matter?

You can ask two simple questions:

1. Does it have mass?
2. Does it take up space?

If the answer to both questions is yes, then it is matter.

Worked Example 1: Is a rock matter?

A rock can be held in your hand. It has mass, which means it has a certain amount of matter in it. It also takes up space.

Answer: Yes, a rock is matter.

Worked Example 2: Is air matter?

Air may be hard to see, but it fills up a basketball or a balloon. That means it takes up space. Air also has mass.

Answer: Yes, air is matter.

Worked Example 3: Is light matter?

Light helps us see things, but it is not a substance with mass and volume like water or wood. It does not take up space as an object does.

Answer: No, light is not matter.

Worked Example 4: Is water matter?

Water can be poured into a cup, so it takes up space. It also has mass. A full bottle of water is heavier than an empty bottle.

Answer: Yes, water is matter.

Comparing matter and non-matter

• Book – matter
• Milk – matter
• Steam – matter
• Air – matter
• Light – not matter
• Sound – not matter

Try thinking like a scientist

Look around the room. Choose an object and ask: Does it have mass? Does it take up space? A desk does. A backpack does. The water in a bottle does. The air in the room does too.

Now think about things that are not matter. The music playing from a speaker is sound, not matter. The brightness from a lamp is light, not matter.

Important idea to remember

Sometimes students think only solids are matter because solids are easy to see and touch. But liquids and gases are matter too. If it has mass and takes up space, it is matter, even if you cannot see it clearly.

Brief Summary

Matter is anything that has mass and takes up space, or volume. Solids, liquids, and gases are all forms of matter. Things like rocks, water, and air are matter. Things like light and sound are not matter because they do not have mass and do not take up space as substances do.

Elements, Compounds, and Mixtures

Everything around us is made of matter. Matter is anything that takes up space.

Some kinds of matter are made of just one kind of tiny building block. Some are made of different kinds joined together. Some are made of different things mixed together.

In this lesson, we will learn about elements, compounds, and mixtures in a simple way.

1. What is an element?

An element is a pure substance made of only one kind of atom.

You can think of an element like a box of all the same kind of bead. Every bead matches.

• Only one kind is there.
• It is a pure substance.
• It is not mixed with other kinds.

Some examples of elements are:

• Gold
• Iron
• Oxygen
• Helium

If you had a jar with only iron in it, that would be an element.

2. What is a compound?

A compound is a pure substance made when two or more kinds of atoms join together.

These atoms are connected in a special way. They stay together as one new substance.

You can think of a compound like red and blue blocks snapped together to make one new shape.

• It has more than one kind of atom.
• The atoms are joined together.
• It is still a pure substance.

Water is a common example of a compound. Water is made from hydrogen and oxygen joined together.

We can show that with symbols:

$$H_2O$$

This means water is made from hydrogen and oxygen atoms joined together.

Salt is another compound. It is made from sodium and chlorine joined together.

3. What is a mixture?

A mixture is made when two or more substances are put together, but they are not joined into a new substance.

In a mixture, each part keeps its own kind of matter.

You can think of a mixture like a bowl of nuts and raisins. They are together, but each one is still itself.

• Two or more substances are together.
• They are not chemically joined.
• Each part keeps its own properties.

Examples of mixtures are:

• Trail mix
• Salad
• Sand and water
• Air

If you mix cereal and marshmallows in a bowl, that is a mixture.

4. How are they different?

Let us compare them.

• Element: one kind of atom only
• Compound: different kinds of atoms joined together
• Mixture: different substances together, but not joined into a new substance

Another way to think about it:

• An element is all the same.
• A compound is different parts connected.
• A mixture is different parts combined without connecting.

5. Pure substances and mixtures

Elements and compounds are both pure substances.

That means they are made of just one kind of substance.

A mixture is not a pure substance because it has different substances together.

6. Looking at examples

Here are some simple clues:

1. If it is only one kind of atom, it is an element.
2. If it is made of different atoms joined together, it is a compound.
3. If different things are together but can still be apart, it is a mixture.

Worked Example 1

Question: A shiny bar is made only of gold. Is it an element, compound, or mixture?

Think: There is only one kind of atom: gold.

Answer: It is an element.

Worked Example 2

Question: Water is made of hydrogen and oxygen joined together. Is it an element, compound, or mixture?

Think: It has two kinds of atoms, and they are joined together.

Answer: It is a compound.

Worked Example 3

Question: A bowl has peanuts, raisins, and cereal pieces stirred together. Is it an element, compound, or mixture?

Think: The parts are together, but each part stays the same.

Answer: It is a mixture.

Worked Example 4

Question: Salt water is made by mixing salt and water. Is it an element, compound, or mixture?

Think: Salt and water are put together. They are not a single new pure substance for this lesson.

Answer: It is a mixture.

7. Helpful picture idea in your mind

Imagine tiny circles.

• If all the circles are the same color, that is an element.
• If two different colored circles are attached in little groups, that is a compound.
• If different colored circles are in the same space but not attached, that is a mixture.

8. Quick check

• Only oxygen atoms: element
• Water: compound
• Salad: mixture
• Only iron atoms: element
• Salt: compound
• Air: mixture

Summary

An element is made of only one kind of atom.

A compound is made of two or more kinds of atoms joined together.

A mixture is made of two or more substances put together without making a new pure substance.

When you look at matter, ask:

• Is it only one kind? Then it may be an element.
• Are different atoms joined together? Then it may be a compound.
• Are different substances just mixed together? Then it may be a mixture.

Observable Physical Properties are features of a material that we can observe, test, or measure without changing what the material is.

For example, a metal spoon can be shiny, hard, and bend a little without breaking. Those are physical properties. The spoon is still metal before and after we observe those properties.

Scientists use physical properties to describe materials and to sort them into groups. In this lesson, we will learn about five important observable physical properties:

• Density
• Luster
• Malleability
• Ductility
• Brittleness

Learning these properties helps us answer questions like:

• Why do some things sink and others float?
• Why are some materials shiny?
• Why can some materials bend, while others snap?
• Why are wires made from metal instead of glass?

Remember: When we talk about observable physical properties, we are talking about how a material looks or acts without turning into a different substance.

1. Density

Density tells us how much matter is packed into a space. A simple way to think about it is: some materials are packed tightly, and some are packed more loosely.

If a material is very dense, its particles are packed closely together. If a material is less dense, its particles are more spread out.

Density helps explain why some objects sink in water and some float.

• If an object is more dense than water, it usually sinks.
• If an object is less dense than water, it usually floats.

Examples:

• A rock usually sinks in water.
• A piece of wood often floats.
• A metal coin sinks.
• A cork floats.

You do not always have to use numbers to think about density in 3rd grade. You can compare objects by watching what happens in water or by noticing how heavy something feels for its size.

2. Luster

Luster means how a material looks when light shines on it.

If something has a lot of luster, it looks shiny. If it does not have much luster, it looks dull, which means not shiny.

Examples of materials with luster:

• Coins
• Aluminum foil
• A polished metal spoon

Examples of materials with little or no luster:

• Wood
• Paper
• Chalk

Luster is something we can often observe just by looking carefully.

3. Malleability

Malleability means a material can be hammered, pressed, or bent into a new shape without breaking.

Some metals are malleable. That is why people can shape them into cans, pans, and foil.

Examples:

• Aluminum foil is malleable because it can be pressed and shaped.
• Soft metal can be flattened instead of snapping.

A material that breaks instead of flattening is not malleable.

4. Ductility

Ductility means a material can be pulled into a thin wire without breaking.

This property is important for making wires that carry electricity.

Examples:

• Copper is ductile, so it is used for wires.
• Some other metals are also ductile.

Glass is not ductile. If you try to pull it into a wire, it will break.

5. Brittleness

Brittleness means a material breaks, cracks, or snaps easily when force is used.

Brittle materials do not bend much before they break.

Examples:

• Dry chalk is brittle.
• Glass is brittle.
• A cracker is brittle because it snaps easily.

Something brittle is very different from something malleable or ductile. Brittle materials break, while malleable and ductile materials change shape without breaking.

How These Properties Help Us Classify Materials

To classify means to sort into groups. Scientists classify materials by looking at their properties.

For example, we can sort materials like this:

• Shiny materials: coins, foil, metal spoon
• Dull materials: paper, wood, chalk
• Brittle materials: glass, chalk, crackers
• Malleable materials: aluminum foil, some metals
• Ductile materials: copper and other wire-making metals
• Less dense materials: cork, many kinds of wood
• More dense materials: rocks, coins

A material can have more than one property. For example, copper can be shiny, ductile, and fairly malleable.

Worked Example 1: Shiny or Dull?

Question: A student looks at a metal spoon and a piece of cardboard. Which material has more luster?

Step 1: Remember that luster means how shiny something looks in the light.

Step 2: Compare the two objects.

• The metal spoon looks shiny.
• The cardboard looks dull.

Answer: The metal spoon has more luster.

Worked Example 2: Sink or Float?

Question: A cork floats in water, but a rock sinks. What does this tell us about density?

Step 1: Remember:

• More dense than water  sinks
• Less dense than water  floats

Step 2: Think about each object.

• The cork floats, so it is less dense than water.
• The rock sinks, so it is more dense than water.

Answer: The cork is less dense than water, and the rock is more dense than water.

Worked Example 3: Bend or Break?

Question: A sheet of aluminum foil can be pressed into a new shape without snapping. Is it malleable or brittle?

Step 1: Remember the meanings.

• Malleable = can be pressed or bent into shape without breaking
• Brittle = breaks easily

Step 2: Look at what happens to the foil.

• It changes shape.
• It does not snap.

Answer: The aluminum foil is malleable.

Worked Example 4: Which Material Should Be Used for a Wire?

Question: A company wants to make a thin wire. Should it choose copper or glass?

Step 1: Remember that a material used for wire needs ductility.

Step 2: Compare the materials.

• Copper is ductile.
• Glass is brittle and breaks easily.

Answer: The company should choose copper because it is ductile.

Helpful Clues for Each Property

• Density: Does it sink or float? Does it feel heavy for its size?
• Luster: Is it shiny or dull?
• Malleability: Can it be pressed or flattened without breaking?
• Ductility: Can it be made into a wire?
• Brittleness: Does it crack or snap easily?

Important Idea: These properties are part of the material itself. They help us identify what a material is like.

For example, if you see a material that is shiny, can bend without breaking, and can be made into wire, it may be a metal.

If you see a material that is dull and breaks easily, it may be brittle, like chalk.

Lets Compare Some Materials

• Chalk: dull, brittle
• Copper wire: shiny, ductile
• Aluminum foil: shiny, malleable
• Rock: usually dull, dense, often sinks in water
• Cork: less dense, floats in water

When we compare materials, we can see that each one has a special set of physical properties.

Summary

Observable physical properties are features we can notice or test without changing a material into something new.

The five properties in this lesson are:

• Density: how tightly matter is packed; helps explain sinking and floating
• Luster: how shiny or dull a material looks
• Malleability: ability to be pressed or bent into shape without breaking
• Ductility: ability to be pulled into a wire
• Brittleness: tendency to crack or break easily

By observing these properties, we can describe, compare, and classify different kinds of matter.

Atomic Theory Foundations helps us understand what all matter is made of. Matter is anything that takes up space and has mass. That means the air in a balloon, the water in a cup, the metal in a spoon, and even your body are all made of matter.

Scientists learned that matter is built from tiny particles too small to see with our eyes. These tiny particles are called atoms. Atoms are the basic building blocks of matter.

Atoms can join together to form molecules. A molecule is made of two or more atoms connected together. Some substances are made of single atoms, and some are made of molecules.

Learning about atoms and molecules helps explain why different materials have different properties. For example, water is a liquid, oxygen is a gas, and iron is a solid. They are all matter, but they are made of different kinds of atoms or different groups of atoms.

Main Idea: All substances are made of atoms, and atoms can join together to make molecules.

1. What is matter?

Matter is anything that has mass and takes up space. If something can be weighed and has a size, it is matter.

• A rock is matter.
• Water is matter.
• Air is matter.
• A pencil is matter.

Light and sound are not matter because they do not take up space in the same way and are not made of atoms.

2. What is an atom?

An atom is an extremely small particle that makes up matter. You cannot see one atom by itself without special tools. Even though atoms are tiny, everything around us is made from huge numbers of them.

You can think of atoms like very tiny building blocks. Just as many bricks can make a wall, many atoms can make a piece of metal, a drop of water, or a leaf.

Different kinds of atoms make different substances. For example, the atoms in gold are different from the atoms in oxygen.

3. What is a molecule?

A molecule forms when atoms join together. Molecules can be made of the same kind of atom or different kinds of atoms.

• Oxygen gas can be made of 2 oxygen atoms joined together.
• Water is made of 2 hydrogen atoms and 1 oxygen atom joined together.

We can show water with a simple formula: \(H_2O\). The small 2 means there are 2 hydrogen atoms. The oxygen has no small number, so that means there is 1 oxygen atom.

So one water molecule has:

• 2 hydrogen atoms
• 1 oxygen atom
• 3 atoms total

4. Atoms and molecules are always moving

Atoms and molecules are not standing still. They are always moving, even in solids. How much they move helps explain the states of matter.

• In solids, particles are packed closely and mostly vibrate in place.
• In liquids, particles are close together but can slide past each other.
• In gases, particles are spread out and move freely.

This is why solids keep their shape, liquids flow, and gases spread out to fill a space.

5. Why do substances have different properties?

A property is a feature you can observe, measure, or describe. Examples include color, hardness, texture, and whether something is a solid, liquid, or gas.

Substances have different properties because they are made of different atoms or different combinations of atoms. The way atoms are arranged also matters.

For example:

• Water is wet and flows because of the way its molecules act.
• Iron is hard and strong because of the way its atoms are packed together.
• Oxygen is a gas because its molecules move freely and spread apart.

6. A model can help us understand

Since atoms are too small to see, scientists use models to help explain them. A model is a simple way to show or think about something.

For example, imagine:

• A single bead = one atom
• Two or more beads snapped together = one molecule

This model is not exactly what atoms look like, but it helps us understand how tiny particles can join together.

7. Important facts to remember

• All matter is made of atoms.
• Atoms are tiny building blocks of matter.
• Atoms can join together to form molecules.
• Different atoms and molecules make different kinds of substances.
• The movement of particles helps explain solids, liquids, and gases.

Worked Example 1: Is it matter?

Question: Which of these are matter: air, a book, light, and water?

Step 1: Remember the rule: matter has mass and takes up space.

Step 2: Check each item.

• Air: yes, it takes up space and has mass.
• Book: yes, it takes up space and has mass.
• Light: no, it is not made of atoms.
• Water: yes, it takes up space and has mass.

Answer: Air, a book, and water are matter. Light is not matter.

Worked Example 2: Atom or molecule?

Question: A particle is made of 3 atoms joined together. Is it an atom or a molecule?

Step 1: An atom is one tiny particle.

Step 2: A molecule is two or more atoms joined together.

Step 3: Since 3 atoms are joined together, it is a molecule.

Answer: It is a molecule.

Worked Example 3: Counting atoms in water

Question: Water is written as \(H_2O\). How many atoms are in one water molecule?

Step 1: The 2 after H means 2 hydrogen atoms.

Step 2: O has no small number, so it means 1 oxygen atom.

Step 3: Add them together.

$$2 + 1 = 3$$

Answer: One water molecule has 3 atoms.

Worked Example 4: Connecting particles to states of matter

Question: In a gas, are particles close together or spread out?

Step 1: Think about how gases act. A gas fills its container.

Step 2: For a gas to spread out, its particles must move freely.

Answer: In a gas, particles are spread out and move freely.

Common mistakes to avoid

• Mistake: Thinking only solids are matter.
  Fix: Liquids and gases are matter too.
• Mistake: Thinking atoms and molecules are the same thing.
  Fix: An atom is one tiny particle. A molecule is two or more atoms joined together.
• Mistake: Thinking air is empty.
  Fix: Air is made of particles and is matter.
• Mistake: Thinking particles stop moving.
  Fix: Particles are always moving.

Try these quick check questions

1. What are all substances made of?
2. What is the difference between an atom and a molecule?
3. Is oxygen in the air matter? Why?
4. Why do different substances have different properties?
5. In which state of matter are particles packed most closely?

Possible answers:

1. All substances are made of atoms.
2. An atom is one tiny particle; a molecule is two or more atoms joined together.
3. Yes, because it has mass and takes up space.
4. Because they are made of different atoms or different combinations of atoms.
5. In a solid.

Summary

Matter is everything that has mass and takes up space. All matter is made of tiny particles called atoms. When atoms join together, they form molecules.

Different atoms and molecules make different substances, and that is why materials can have different properties. Understanding atoms and molecules helps us explain the world around us, from the air we breathe to the water we drink.

States of Matter and Plasma

Everything around us is made of matter. Matter is anything that takes up space and has mass. A rock is matter. Water is matter. Air is matter too, even though we cannot see it.

Matter can be found in different states. The main states we will learn about are solid, liquid, gas, and plasma. Each state acts in its own special way.

To understand why, it helps to imagine that all matter is made of tiny pieces called particles. These particles are much too small to see, but they are always there. The way the particles are arranged and how they move helps decide whether matter is a solid, liquid, gas, or plasma.

1. Solids

A solid has its own shape and its own size. If you put a book on a table, it stays the same shape. If you pick up an ice cube, it keeps its shape too.

In a solid, the particles are packed very close together. They do not move around freely. Instead, they mostly wiggle in place. Because the particles are so close together, solids are usually hard to squeeze.

• A solid has a definite shape.
• A solid has a definite volume (amount of space it takes up).
• Its particles are close together.
• It is not easy to compress, or squeeze smaller.

Examples of solids include:

• rock
• pencil
• ice
• desk

2. Liquids

A liquid does not have its own shape, but it does have its own volume. This means a liquid can change shape to fit its container. Water in a cup takes the shape of the cup. Juice in a bottle takes the shape of the bottle.

In a liquid, the particles are still close together, but they can slide past one another. That is why liquids can flow.

• A liquid has no definite shape.
• A liquid has a definite volume.
• Its particles are close together but can move past each other.
• It is not easy to compress.

Examples of liquids include:

• water
• milk
• oil
• rain

3. Gases

A gas has no definite shape and no definite volume. A gas spreads out to fill the space around it. Air in a balloon fills the balloon. Air in a room spreads through the whole room.

In a gas, the particles are much farther apart than in solids or liquids. They move freely and quickly in many directions. Because there is so much space between the particles, gases can be squeezed into a smaller space more easily. This is called being compressible.

• A gas has no definite shape.
• A gas has no definite volume.
• Its particles are far apart and move freely.
• It can be compressed more easily than solids and liquids.

Examples of gases include:

• air
• oxygen
• helium in a balloon
• steam

4. Plasma

Plasma is a special state of matter. It is like a gas, but it has much more energy. In plasma, tiny particles have so much energy that they can carry electric charge.

Plasma is not as common in our homes as solids, liquids, and gases, but it is very important. In fact, the Sun and other stars are made of plasma.

Examples of plasma include:

• the Sun
• stars
• lightning
• some glowing signs and special lamps

You do not need to remember every tiny detail about plasma. The most important idea is that plasma is a very energetic state of matter, and it is different from an ordinary gas.

How the particles are arranged

Here is an easy way to compare the four states:

• Solid: particles are tightly packed and mostly stay in place.
• Liquid: particles are close together and slide past each other.
• Gas: particles are far apart and move around freely.
• Plasma: particles move freely like a gas, but they have much more energy.

Shape and volume

Let us compare how the states of matter keep their shape and volume.

• Solid: keeps its shape and volume.
• Liquid: changes shape, but keeps its volume.
• Gas: changes shape and changes volume to fill its space.
• Plasma: also does not keep a fixed shape or volume.

Compressibility

Compressibility means how easily something can be squeezed into a smaller space.

Solids are very hard to squeeze because their particles are already packed tightly. Liquids are also hard to squeeze because their particles are still close together. Gases are much easier to squeeze because there is more empty space between particles. Plasma acts more like a gas in this way.

• Solid: very hard to compress
• Liquid: hard to compress
• Gas: easy to compress compared with solids and liquids
• Plasma: can spread out like a gas

Changes in state

Matter can change from one state to another when it gains or loses heat. These are called changes of state.

• Melting: solid to liquid
• Freezing: liquid to solid
• Evaporation: liquid to gas
• Condensation: gas to liquid

For example, an ice cube can melt into water. Water can evaporate and become water vapor in the air. Water vapor can cool and turn back into liquid drops.

Sometimes if matter gets a very large amount of energy, a gas can become plasma. This happens in stars and lightning.

Worked Example 1: Sorting common objects

Question: Is each item a solid, liquid, gas, or plasma: a chair, orange juice, air, and the Sun?

Step 1: Think about shape and volume.

• A chair keeps its own shape, so it is a solid.
• Orange juice pours and takes the shape of its cup, so it is a liquid.
• Air spreads out and fills space, so it is a gas.
• The Sun is made of very energetic matter, so it is plasma.

Answer: Chair = solid, orange juice = liquid, air = gas, Sun = plasma.

Worked Example 2: Thinking about particles

Question: Which state has particles packed closest together: solid, liquid, or gas?

Step 1: Remember how particles act in each state.

• In a solid, particles are tightly packed.
• In a liquid, particles are close but can move.
• In a gas, particles are far apart.

Answer: A solid has particles packed closest together.

Worked Example 3: Which can be compressed?

Question: You have a rock, a cup of water, and air in a syringe. Which one is easiest to squeeze into a smaller space?

Step 1: Think about particle spacing.

• The rock is a solid, so its particles are very close together.
• The water is a liquid, so its particles are also close together.
• The air is a gas, so its particles are far apart.

Step 2: Choose the one with the most space between particles.

Answer: The air is easiest to compress.

Worked Example 4: A change of state

Question: An ice cube is left on a plate and turns into a puddle of water. What change of state happened?

Step 1: Identify the first state. Ice is a solid.

Step 2: Identify the new state. Water is a liquid.

Step 3: Name the change from solid to liquid.

Answer: The ice melted. Melting is a change from solid to liquid.

Helpful way to remember

1. Solid = keeps its shape
2. Liquid = flows and takes the shape of its container
3. Gas = spreads out to fill space
4. Plasma = very energetic matter, like in the Sun and lightning

Quick check

• Does a solid keep its shape? Yes.
• Does a liquid keep its volume? Yes.
• Can a gas fill a container? Yes.
• Is plasma found in stars? Yes.

Summary

Matter is anything that takes up space and has mass. Matter can be a solid, liquid, gas, or plasma. These states are different because their particles are arranged differently and move in different ways.

Solids keep their shape and are hard to compress. Liquids flow and take the shape of their container, but they keep their volume. Gases spread out to fill space and are easier to compress. Plasma is a very energetic state of matter found in the Sun, stars, lightning, and some lamps.

The Particle Nature of Matter

Everything around us is made of matter. Matter is anything that takes up space and has weight. A rock is matter. Water is matter. Air is matter too.

But what is matter made of? Matter is made of very tiny pieces called particles. These particles are so small that we cannot see them with just our eyes.

You can think of particles like teeny-tiny building blocks. They join together to make all the things we see and touch every day.

What are particles?

Scientists use names like atoms and molecules for these tiny particles. For us, it is enough to remember this: all matter is made of tiny particles.

These particles are always moving. Even when something looks still, the particles inside it are moving.

How particles act in solids, liquids, and gases

Matter can be a solid, a liquid, or a gas. The particles in each state move in different ways.

• Solid: The particles are packed close together. They wiggle in place, but they do not move around very much.
• Liquid: The particles are still close together, but they can slide past one another.
• Gas: The particles are spread far apart and move around quickly.

This is why solids usually keep their shape, liquids can flow, and gases spread out to fill space.

Solids

In a solid, the particles are very close together. They stay in their spots and only shake or wiggle.

That is why a book keeps its shape. A block of ice keeps its shape too. The particles are packed tightly.

Liquids

In a liquid, the particles are close, but not stuck in one place. They can move and slide around each other.

That is why water can be poured into a cup. If you pour the same water into a bowl, it changes shape to fit the bowl.

Gases

In a gas, the particles are much farther apart. They move quickly in all directions.

That is why air spreads out and fills a room. You cannot usually see the particles, but they are there.

Particles are always moving

A very important idea is this: particles are always moving. They move in solids, liquids, and gases.

In solids, particles move the least. In liquids, they move more. In gases, they move the most.

When particles get more energy, they move faster. When they have less energy, they move slower.

Heat changes particle motion

Heat is a kind of energy. When matter is heated, its particles usually move faster.

When particles move faster, matter can change from one state to another. For example, ice can melt into water. Water can heat up and become water vapor, which is a gas.

When matter cools, particles slow down. Water vapor can cool and turn back into liquid water. Liquid water can cool even more and freeze into ice.

Easy picture in your mind

• Solid: particles packed tight, wiggling in place
• Liquid: particles close together, sliding past each other
• Gas: particles far apart, moving fast

Examples from everyday life

• An ice cube is a solid. Its particles are packed close together.
• A glass of juice is a liquid. Its particles can move past each other.
• The air in a balloon is a gas. Its particles spread out and fill the balloon.

Worked Example 1

Question: A wooden table keeps the same shape every day. What does this tell us about its particles?

Step 1: A table is a solid.

Step 2: In solids, particles are packed close together.

Step 3: The particles wiggle in place, but do not slide around much.

Answer: The table’s particles are packed tightly and only move a little in place.

Worked Example 2

Question: Water can be poured from a bottle into a cup. What does this show about the particles in water?

Step 1: Water is a liquid.

Step 2: In liquids, particles are close together.

Step 3: The particles can slide past one another.

Answer: Water’s particles can move around each other, so water can flow and change shape.

Worked Example 3

Question: Air fills up a balloon. What does this tell us about gas particles?

Step 1: Air is a gas.

Step 2: Gas particles are far apart.

Step 3: They move quickly and spread out to fill space.

Answer: Gas particles move around and spread out, so they fill the balloon.

Worked Example 4

Question: An ice cube sits in the sun and turns into liquid water. What happened to the particles?

Step 1: The ice got heat from the sun.

Step 2: Heat made the particles move faster.

Step 3: The tightly packed particles in the solid began to move more and slide past each other.

Answer: The particles gained energy, moved faster, and the solid ice melted into liquid water.

Things to remember

1. All matter is made of tiny particles.
2. These particles are always moving.
3. Particles in solids, liquids, and gases move in different ways.
4. Heat can make particles move faster.
5. Cooling can make particles move slower.

Quick check

• Does a solid keep its shape? Yes.
• Can a liquid be poured? Yes.
• Does a gas spread out to fill space? Yes.
• Are particles always moving? Yes.

Summary

All matter is made of tiny particles called atoms and molecules. These particles are always moving, even if we cannot see them.

In solids, particles are packed tightly and wiggle in place. In liquids, particles stay close but slide past each other. In gases, particles are far apart and move quickly.

Heat gives particles more energy, so they move faster. Cooling makes them move slower. This helps explain why matter can change from a solid to a liquid to a gas, and back again.

Mass vs. Weight

Have you ever heard someone say, “How much do you weigh?” In everyday life, people often use the words mass and weight as if they mean the same thing. In science, they are not the same.

Learning the difference is important because mass tells us how much matter is in an object, while weight tells us how strongly gravity is pulling on that object.

Let’s learn how mass and weight are different, how they are measured, and why an object’s mass stays the same even when its weight changes.

What is mass?

Mass is the amount of matter in an object. Matter is the “stuff” that makes up everything around us.

A bowling ball has more matter than a tennis ball, so it has more mass. A full backpack has more matter than an empty backpack, so it has more mass too.

Mass does not depend on where the object is. If you take a rock from Earth to the Moon, it still has the same amount of matter, so its mass stays the same.

Mass is usually measured in grams (g) or kilograms (kg).

• A paper clip might have a mass of about 1 gram.
• A textbook might have a mass of about 1 kilogram.

Scientists often measure mass with a balance.

What is weight?

Weight is the pull of gravity on an object.

Gravity is the force that pulls objects toward Earth. When you stand on a scale, the scale is measuring how strongly Earth’s gravity is pulling on you. That pull is your weight.

Weight can change if gravity changes. For example, the Moon has less gravity than Earth, so the same person would weigh less on the Moon.

Weight is often measured with a scale. In science, weight is a force, but for now the important idea is this: weight depends on gravity.

The biggest difference

• Mass = how much matter is in an object
• Weight = how strongly gravity pulls on that object

This means:

• An object’s mass stays the same unless matter is added or taken away.
• An object’s weight can change if gravity changes.

Think about a backpack

Imagine you have a backpack full of books.

The mass of the backpack is the total amount of matter in the backpack and books.

The weight of the backpack is how hard gravity pulls down on it.

If you take the same backpack to the Moon:

• The books are still inside.
• The amount of matter is still the same.
• So the mass stays the same.
• But the Moon’s gravity is weaker.
• So the weight becomes less.

Mass and weight are related

Mass and weight are different, but they are connected. If an object has more mass, gravity usually pulls on it more strongly, so it usually has more weight too.

For example, a bicycle has more mass than an apple. Because it has more mass, Earth’s gravity pulls on it more, so it weighs more.

Still, remember: they are not exactly the same idea.

A simple way to remember

• Mass = matter
• Weight = gravity’s pull

You can also remember it like this:

Mass is what is inside the object.

Weight is what gravity does to the object.

How are they measured?

• Mass is measured in grams or kilograms.
• Weight is measured with a scale because it depends on gravity.

In many classrooms, students use a balance to compare mass and a scale to measure weight.

Worked Example 1: Apple and watermelon

An apple has less matter than a watermelon.

Question: Which has greater mass? Which has greater weight on Earth?

Step 1: Think about matter. The watermelon has much more matter than the apple.

Step 2: So the watermelon has greater mass.

Step 3: On Earth, more mass usually means gravity pulls more strongly.

Answer: The watermelon has greater mass and greater weight on Earth.

Worked Example 2: Same object on Earth and the Moon

A toy robot has a mass of 2 kilograms on Earth.

Question: What happens to its mass and weight if it is taken to the Moon?

Step 1: Ask whether the amount of matter changes. It does not.

Step 2: So the mass stays 2 kilograms.

Step 3: Ask whether gravity changes. Yes, the Moon has weaker gravity than Earth.

Answer: The robot’s mass stays the same, but its weight becomes less on the Moon.

Worked Example 3: Adding books to a bag

A bag has 3 books in it. Then 2 more books are added.

Question: What happens to the bag’s mass and weight on Earth?

Step 1: Adding books adds more matter.

Step 2: More matter means the mass increases.

Step 3: Since there is more mass, Earth’s gravity pulls more strongly.

Answer: Both the mass and the weight increase.

Worked Example 4: True or false

Statement: “If an astronaut goes to the Moon, her mass becomes smaller.”

Step 1: Mass is the amount of matter in her body.

Step 2: Going to the Moon does not remove matter from her body.

Step 3: Only gravity changes.

Answer: False. Her mass stays the same, but her weight becomes smaller.

Common mistakes to avoid

• Do not say mass and weight always mean the same thing in science.
• Do not forget that mass stays the same if the amount of matter stays the same.
• Do not forget that weight changes when gravity changes.

Quick compare chart

• Mass: amount of matter
• Weight: pull of gravity
• Mass: measured in grams or kilograms
• Weight: measured with a scale
• Mass: stays the same in different places
• Weight: can change in different places

Mini practice

1. A soccer ball is taken from Earth to the Moon. Does its mass change?
2. Does its weight change?
3. If sand is poured into a bucket, what happens to the bucket’s mass?
4. What happens to its weight on Earth?

Answers:

1. No, its mass does not change.
2. Yes, its weight changes and becomes less.
3. Its mass increases.
4. Its weight also increases.

Summary

Mass is the amount of matter in an object. Weight is the pull of gravity on that object.

Mass stays the same unless matter is added or removed. Weight can change when gravity changes.

If you remember mass = matter and weight = gravity’s pull, you will be able to tell them apart.

Volume and Displacement

Everything around us is made of matter. Matter takes up space. The amount of space an object takes up is called its volume.

In this lesson, you will learn two important ways to find volume:

• Finding the volume of regular-shaped objects using measurements and a formula
• Finding the volume of irregular-shaped objects using water displacement

These skills help scientists describe matter and compare objects by how much space they fill.

What Is Volume?

Volume is the amount of space inside an object or the amount of space an object takes up.

We measure volume in cubic units. A cubic unit is a tiny cube used to fill space.

• inches cubed: \(in^3\)
• centimeters cubed: \(cm^3\)
• meters cubed: \(m^3\)

If a box has a volume of \(24\;cm^3\), that means it would take 24 little cubes that are each \(1\;cm\) long, \(1\;cm\) wide, and \(1\;cm\) tall to fill it.

Volume of Regular Objects

A regular object has a shape that can be measured easily, like a box, cube, or rectangular prism.

To find the volume of a rectangular prism, multiply:

Or you can write it as:

This works because you are finding how many tiny cubes fit inside the object.

Steps for Finding Volume of a Regular Object

1. Measure the length.
2. Measure the width.
3. Measure the height.
4. Multiply the three numbers.
5. Write the answer in cubic units.

Worked Example 1: Finding the Volume of a Box

A box is \(4\;cm\) long, \(3\;cm\) wide, and \(2\;cm\) high.

Use the formula:

Substitute the numbers:

The volume is \(24\;cm^3\).

This means the box takes up the same space as 24 cubes that each have a side length of 1 centimeter.

Worked Example 2: A Cube

A cube has sides that are all the same length. If each side is \(5\;cm\), then:

The volume is \(125\;cm^3\).

Why Do We Need Displacement?

Some objects do not have a regular shape. A rock, key, shell, or toy figure may be bumpy or curved. These are called irregular objects.

For irregular objects, it is hard to measure length, width, and height in a useful way. Instead, we can find volume by using displacement.

What Is Displacement?

Displacement happens when an object is placed in water and pushes some of the water out of the way.

The amount the water level rises is equal to the volume of the object under the water.

This is called the water displacement method.

How to Find Volume Using Water Displacement

1. Pour water into a measuring container, like a graduated cylinder.
2. Record the starting volume of the water.
3. Carefully place the object into the water.
4. Record the new volume of the water.
5. Subtract the starting volume from the new volume.

Use this equation:

Important: The object must sink fully under the water for this method to work well. Also, be careful not to spill water.

Worked Example 3: Finding the Volume of a Rock

A graduated cylinder starts with \(30\;mL\) of water. After a rock is placed in the cylinder, the water rises to \(42\;mL\).

Subtract:

The rock has a volume of \(12\;mL\).

In science, for water displacement, \(1\;mL\) of displaced water matches \(1\;cm^3\) of volume. So the rock's volume is also \(12\;cm^3\).

Worked Example 4: Comparing Two Objects

An empty measuring container is filled to \(50\;mL\). A shell is placed in the water, and the level rises to \(58\;mL\). Then a different object is tested, and the water rises from \(50\;mL\) to \(65\;mL\).

First object:

The shell has a volume of \(8\;mL\) or \(8\;cm^3\).

Second object:

The second object has a volume of \(15\;mL\) or \(15\;cm^3\).

Since \(15 > 8\), the second object takes up more space.

Regular vs. Irregular Objects

• Regular objects: Use measurements and a formula.
• Irregular objects: Use water displacement.

Examples of regular objects include:

• a shoebox
• a cube block
• a book-shaped box

Examples of irregular objects include:

• a rock
• a key
• a seashell

Tips for Measuring Carefully

• Use the same unit for all measurements.
• Multiply carefully when finding volume of regular shapes.
• Read the water level closely when using displacement.
• Subtract in the correct order: final water level minus starting water level.
• Remember to label your answer with the correct unit.

Common Mistakes to Avoid

• Forgetting one of the three measurements: length, width, or height
• Writing square units instead of cubic units
• Adding instead of multiplying for regular objects
• Subtracting the water levels in the wrong order
• Trying to use displacement with an object that is not fully underwater

How Volume Connects to Matter

Volume is one of the properties scientists use to describe matter. Since matter takes up space, every piece of matter has volume.

By measuring volume, we can learn more about objects, compare them, and describe their physical properties.

Brief Summary

Volume is the amount of space an object takes up. For regular objects like boxes, find volume by multiplying length, width, and height.

For irregular objects like rocks, use water displacement. Measure how much the water level rises, and that change tells you the object's volume.

When you know how to measure volume, you can better understand matter and its properties.

Solubility and Saturation

Have you ever stirred sugar into water and watched it seem to disappear? It did not really vanish. The sugar mixed into the water and made a solution.

In science, some things can mix into a liquid so well that they seem to disappear. This is called dissolving. Today we will learn about solubility and saturation.

Solubility means how well something can dissolve in a liquid. The thing being dissolved is called the solute. The liquid doing the dissolving is called the solvent.

• Sugar is a solute when it is mixed into water.
• Water is the solvent.
• Together they make a solution.

Not everything dissolves the same way. Some things dissolve easily. Some dissolve slowly. Some do not dissolve much at all.

• Sugar dissolves in water.
• Salt dissolves in water.
• Sand does not dissolve well in water.
• Pepper does not dissolve well in water.

When a solute dissolves, the tiny pieces spread out in the solvent. That is why we may not see the solute anymore, even though it is still there.

We can often help a solute dissolve by stirring. Stirring mixes the solute and solvent together.

We can also help some solutes dissolve by using warm water. Many solids, like sugar, dissolve better in warmer water than in cold water.

This means temperature can matter. Temperature tells how hot or cold something is. A warmer solvent can sometimes hold more of a solute.

Now let us learn about saturation. A solution is saturated when no more solute can dissolve in it.

Imagine adding spoon after spoon of sugar to a cup of water. At first, the sugar dissolves. But after a while, you may see sugar sitting at the bottom. That means the water has reached saturation.

When the extra solute stays at the bottom and does not disappear, the solution is full. It cannot dissolve more at that temperature.

Important idea: A saturated solution is not broken. It is just holding as much solute as it can.

Let us look at the steps:

1. Add a solute to a solvent.
2. Stir and watch if it dissolves.
3. Add more solute.
4. If it keeps dissolving, the solution is not saturated yet.
5. If some stays undissolved, the solution is saturated.

Temperature can change how much dissolves. For many solids:

• Warmer water can dissolve more.
• Cooler water may dissolve less.

So, if a cup of warm water is saturated with sugar, adding more sugar will not help unless something changes. But if the water gets warmer, it may be able to dissolve a little more.

Here is a simple way to think about it:

• Solubility = how much can dissolve
• Saturation = the point when no more can dissolve

We can show a small math idea with spoons. Suppose 1 cup of water can dissolve 3 spoons of sugar.

Then we can think:

$$1\ \text{cup water} \rightarrow 3\ \text{spoons sugar}$$

If we add 2 spoons, all of it may dissolve. If we add 3 spoons, it may still dissolve. If we add 4 spoons, 1 spoon may be left over.

That means:

$$4 - 3 = 1$$

So 1 spoon would stay undissolved if the water is already full.

Worked Example 1: Sugar in Water

Mia puts 1 spoon of sugar into a glass of water and stirs. The sugar disappears. What happened?

Answer: The sugar dissolved. Sugar is the solute, and water is the solvent. Together they made a solution.

Worked Example 2: Sand in Water

Leo puts sand into water and stirs. The sand sinks to the bottom. Did it dissolve well?

Answer: No. Sand does not dissolve well in water. It stays as little pieces you can still see.

Worked Example 3: Full of Sugar

A cup of water can dissolve 3 spoons of sugar. Ava adds 3 spoons, and they dissolve. Then she adds 1 more spoon. It stays at the bottom.

Is the solution saturated?

Answer: Yes. The water already dissolved as much sugar as it could. The extra sugar staying at the bottom shows the solution is saturated.

We can write:

$$3 + 1 = 4$$

But only 3 spoons dissolved, so 1 spoon did not dissolve.

Worked Example 4: Warm Water and Cold Water

One cup of cold water dissolves 2 spoons of sugar. One cup of warm water dissolves 4 spoons of sugar. Which one has greater solubility for sugar?

Answer: The warm water. It can dissolve more sugar.

We can compare:

$$4 > 2$$

Since 4 is greater than 2, the warm water dissolved more.

Things to Remember

• A solute is what gets dissolved.
• A solvent is the liquid that does the dissolving.
• A solution is the mixture that forms.
• Solubility tells how well something dissolves.
• Saturation means no more can dissolve.
• Warm water can often dissolve more solid stuff than cold water.

You can test this idea at home or in class with help from an adult. Try sugar in cold water and sugar in warm water. Stir both. Watch which one dissolves more easily.

Science helps us describe what we see. When something disappears into a liquid, it may be dissolving. When extra solid stays behind, the liquid may already be saturated.

Brief Summary

Solubility is how well a solute dissolves in a solvent. Saturation is when the solvent cannot dissolve any more solute. Sugar and salt dissolve in water, but sand does not dissolve well. Warmer water can often dissolve more solid material than colder water.

Density and Buoyancy are two big ideas that help us understand why some things float and some things sink.

Have you ever wondered why a huge ship can float on water, but a small rock sinks? The answer has to do with density and buoyancy.

In this lesson, you will learn what density means, how to calculate it, and how to use density to predict whether an object will float or sink in a fluid like water.

What Is Density?

Density tells us how much matter is packed into a certain amount of space.

An object with a lot of matter packed into a small space has high density. An object with less matter in the same amount of space has low density.

Another way to say this is:

• Mass is how much matter is in an object.
• Volume is how much space an object takes up.
• Density compares mass and volume.

The formula for density is:

$$\text{density} = \frac{\text{mass}}{\text{volume}}$$

You may also see it written as:

$$d = \frac{m}{v}$$

This means you divide the mass by the volume.

Understanding the Formula

If two objects are the same size, the one with more mass is denser.

If two objects have the same mass, the one that takes up less space is denser.

For example, imagine a small metal cube and a same-size foam cube. The metal cube has more matter packed inside, so it has a greater density.

Units for Density

Density is often measured in grams per cubic centimeter or grams per milliliter.

You might see:

• grams per cubic centimeter: \(g/cm^3\)
• grams per milliliter: \(g/mL\)

For 5th Grade, the most important thing is to remember that density is mass divided by volume.

What Is Buoyancy?

Buoyancy is the upward push a fluid gives to an object.

A fluid is something that can flow, like water, juice, or air. In this lesson, we will mostly talk about objects in water.

Water pushes up on objects that are in it. This upward push is called the buoyant force.

If the upward push is strong enough, the object floats. If it is not strong enough, the object sinks.

How Density Helps Us Predict Floating and Sinking

To predict whether an object will float or sink in water, compare the object’s density to the density of water.

• If an object is less dense than water, it will float.
• If an object is more dense than water, it will sink.
• If an object has about the same density as water, it may stay suspended or barely float.

Water has a density of about \(1 \, g/mL\).

That means:

• Less than \(1 \ , g/mL\) → likely floats in water
• Greater than \(1 \ , g/mL\) → likely sinks in water

Why Shape Can Matter Too

You may know that a ball of clay sinks, but a clay boat can float. Why?

When the clay is shaped like a boat, it spreads out and takes up more space. This changes the overall density of the clay and the air inside the boat shape.

This is why large ships made of metal can float. Even though metal is dense, the ship has a shape full of air and takes up a lot of space, so its overall density can be less than water.

Worked Example 1: Finding Density

A block has a mass of 12 grams and a volume of 4 milliliters. What is its density?

Use the formula:

$$d = \frac{m}{v}$$

Substitute the numbers:

$$d = \frac{12}{4} = 3$$

The density is \(3 \, g/mL\).

Since \(3 \ , g/mL\) is greater than \(1 \ , g/mL\), this block would sink in water.

Worked Example 2: Predict Float or Sink

A toy has a density of \(0.8 \, g/mL\). Will it float or sink in water?

Compare \(0.8\) to water’s density, which is about \(1\).

• Object density = \(0.8 \, g/mL\)
• Water density = \(1 \, g/mL\)

Because \(0.8\) is less than \(1\), the toy is less dense than water.

Answer: The toy will float.

Worked Example 3: Another Density Calculation

A rock has a mass of 18 grams and a volume of 6 milliliters. Will it float or sink in water?

Step 1: Find the density.

$$d = \frac{m}{v} = \frac{18}{6} = 3 \ , g/mL$$

Step 2: Compare to water.

Since \(3 \ , g/mL\) is greater than \(1 \ , g/mL\), the rock is more dense than water.

Answer: The rock will sink.

Worked Example 4: Compare Two Objects

Object A has a mass of 10 grams and a volume of 5 milliliters.

Object B has a mass of 10 grams and a volume of 20 milliliters.

Which object is denser, and which one is more likely to float in water?

First, find the density of each object.

For Object A:

$$d = \frac{10}{5} = 2 \ , g/mL$$

For Object B:

$$d = \frac{10}{20} = 0.5 \ , g/mL$$

Now compare them:

• Object A: \(2 \, g/mL\)
• Object B: \(0.5 \, g/mL\)

Object A is denser because \(2\) is greater than \(0.5\).

Compared to water:

• Object A is more dense than water, so it will sink.
• Object B is less dense than water, so it will float.

Easy Ways to Think About Density

• Heavy for its size usually means higher density.
• Light for its size usually means lower density.
• Small objects can sink if they are very dense.
• Large objects can float if their overall density is low enough.

Real-Life Examples

• A rock usually sinks because it is more dense than water.
• Wood often floats because it is less dense than water.
• Ice floats on liquid water because ice is less dense than water.
• Ships float because their shape helps lower their overall density.
• A life jacket helps a person float by adding buoyancy.

Common Mistakes to Watch Out For

• Mistake 1: Thinking heavier objects always sink. A heavy ship can float if its overall density is less than water.
• Mistake 2: Thinking small objects always float. A tiny pebble can sink if it is more dense than water.
• Mistake 3: Mixing up mass and volume. Mass is how much matter there is. Volume is how much space it takes up.
• Mistake 4: Forgetting to divide mass by volume when finding density.

Steps for Solving Density and Buoyancy Problems

1. Find the mass of the object.
2. Find the volume of the object.
3. Use the formula $$d = \frac{m}{v}$$
4. Compare the density to water, which is about \(1 \, g/mL\).
5. Decide if the object will float or sink.

Quick Practice Thinking

If an object has a density of \(0.4 \, g/mL\), it will float in water.

If an object has a density of \(1.7 \, g/mL\), it will sink in water.

If an object has the same density as water, it may stay in the middle or barely float.

Brief Summary

Density tells us how much matter is packed into a certain space. You can calculate density by dividing mass by volume:

$$d = \frac{m}{v}$$

Buoyancy is the upward push from a fluid like water. An object usually floats if it is less dense than water and sinks if it is more dense than water.

When you know an object’s mass and volume, you can find its density and make a good prediction about whether it will float or sink.

Physical Properties of Matter

Everything around you is made of matter. Matter is anything that has mass and takes up space. A chair, a pencil, water, air, and even your backpack are all matter.

Scientists study matter by observing and testing its properties. A property is something we can notice, measure, or test. In this lesson, you will learn about physical properties of matter. These are features we can observe or test without changing what the material is made of.

For example, you can test whether a spoon is magnetic or whether a wire can carry electricity. Even after the test, the spoon is still metal and the wire is still wire. That means you are studying a physical property.

What Are Physical Properties?

Physical properties are characteristics of a material that can be observed, measured, or tested without making a new substance. These properties help us sort and identify materials.

Some physical properties you may already know are color, size, shape, texture, and mass. In this lesson, we will focus on four important physical properties:

• Malleability
• Ductility
• Thermal conductivity
• Electrical conductivity
• Magnetism

1. Malleability

Malleability is the ability of a material to be hammered, pressed, or rolled into a new shape without breaking.

A malleable material can be flattened or bent into shapes. Many metals are malleable. For example, aluminum can be pressed into thin sheets, like aluminum foil.

Materials that are not malleable may crack, snap, or shatter when you try to change their shape. Glass is not malleable because it breaks instead of flattening.

Examples of malleable materials:

• Aluminum foil
• Copper sheet
• Gold

Examples of materials that are not malleable:

• Glass
• Wood
• Hard plastic

2. Ductility

Ductility is the ability of a material to be pulled or stretched into a wire without breaking.

This property is important when people make wires for electricity. Copper is ductile, so it can be drawn into long, thin wires. That is one reason copper is often used in electrical wires.

A material that is not ductile will snap or crumble instead of stretching into wire.

Examples of ductile materials:

• Copper
• Aluminum
• Some other metals

Examples of materials that are not ductile:

• Glass
• Rubber bands do stretch, but they are not usually drawn into metal-like wires
• Wood

Malleability and Ductility Are Different

These two properties may sound alike, but they are not the same.

• Malleability means a material can be shaped by pressing or hammering.
• Ductility means a material can be pulled into wire.

A material can have both properties. Many metals, like copper and aluminum, are both malleable and ductile.

3. Thermal Conductivity

Thermal conductivity is how well a material allows heat to move through it.

Materials that let heat move easily are called good thermal conductors. Many metals are good conductors of heat. That is why a metal spoon in hot soup gets warm quickly.

Materials that do not let heat move easily are called insulators. Wood, plastic, rubber, and foam are often good insulators. That is why cooking pots may have plastic or wooden handles. These handles help protect your hands from heat.

Examples of good thermal conductors:

• Metal spoon
• Aluminum pan
• Copper pot

Examples of thermal insulators:

• Wooden spoon
• Plastic handle
• Oven mitt

4. Electrical Conductivity

Electrical conductivity is how well a material allows electricity to pass through it.

Materials that let electricity move through them easily are called electrical conductors. Many metals are electrical conductors. Copper is commonly used in wires because electricity can travel through it well.

Materials that do not let electricity pass through them easily are called electrical insulators. Plastic, rubber, glass, and wood are common insulators.

Insulators are important for safety. For example, the plastic covering around a wire helps protect you from the electricity inside.

Examples of electrical conductors:

• Copper wire
• Aluminum foil
• Metal paper clip

Examples of electrical insulators:

• Plastic
• Rubber
• Glass

5. Magnetism

Magnetism is the ability of a material to be attracted to a magnet or to act like a magnet.

Not all metals are magnetic. This is important to remember. Iron is magnetic, and steel often is too because it contains iron. But metals like aluminum and copper are usually not magnetic.

You can test magnetism by bringing a magnet close to an object. If the object is pulled toward the magnet, it is magnetic.

Examples of magnetic materials:

• Iron nail
• Steel paper clip
• Some cans made with steel

Examples of materials that are not magnetic:

• Aluminum can
• Copper wire
• Plastic ruler

How Scientists Test Physical Properties

Scientists use careful observations and simple tests to learn about materials. They compare results and use the data to classify objects.

Here are some ways to test physical properties:

1. Test malleability: Gently press or hammer a material to see if it changes shape without breaking.
2. Test ductility: See whether a material can be drawn or stretched into a thin wire.
3. Test thermal conductivity: Compare how quickly different materials get warm when near heat.
4. Test electrical conductivity: Use a simple circuit to see whether electricity can pass through the material.
5. Test magnetism: Bring a magnet close to the object and observe what happens.

When testing materials, safety comes first. Students should only do tests with an adult or teacher, especially when heat or electricity is involved.

Why These Properties Matter

Knowing physical properties helps people choose the right material for a job.

• Cookware is often made of metal because metal transfers heat well.
• Wire is often made of copper because copper is ductile and conducts electricity well.
• Tool handles may be covered with rubber or plastic because these materials are insulators.
• Aluminum foil is useful because aluminum is malleable.
• Magnets can be used to sort certain metals because some materials are magnetic and others are not.

Classifying Materials

To classify means to group things by their properties. Scientists often classify materials based on what they do in tests.

For example, if a material is shiny, can be bent, carries electricity, and may be magnetic, it may be a metal. If a material does not carry electricity well and is not magnetic, it may be plastic, rubber, or wood.

You do not always need just one test. Scientists often use more than one property to identify a material.

Worked Example 1: Identifying Malleability

Question: A student presses on two materials. Material A flattens into a thin shape. Material B cracks into pieces. Which material is malleable?

Step 1: Remember the meaning of malleability.

Malleability means a material can be pressed or hammered into a new shape without breaking.

Step 2: Compare the materials.

• Material A flattens.
• Material B cracks.

Answer: Material A is malleable because it changes shape without breaking.

Worked Example 2: Choosing a Material for Wire

Question: Which property is most important if you want to make a long, thin wire: malleability or ductility?

Step 1: Recall the meanings.

• Malleability = can be pressed into shape.
• Ductility = can be pulled into wire.

Step 2: Match the property to the task.

A long, thin wire must be pulled out without breaking.

Answer: Ductility is the most important property for making wire.

Worked Example 3: Conductors and Insulators

Question: A metal spoon and a wooden spoon are placed in warm soup. After a few minutes, the metal spoon feels hotter than the wooden spoon. What does this show?

Step 1: Think about how heat moves.

If one material gets hot quickly, heat is moving through it well.

Step 2: Compare the two spoons.

• The metal spoon gets hotter faster.
• The wooden spoon stays cooler.

Answer: The metal spoon is a better thermal conductor. The wooden spoon is a better insulator.

Worked Example 4: Using More Than One Property

Question: A material can be pulled into wire, carries electricity well, and is not attracted to a magnet. What might it be?

Step 1: Look at each clue.

• Can be pulled into wire 6 ductile
• Carries electricity well 6 electrical conductor
• Not attracted to a magnet 6 not magnetic

Step 2: Think of a common material with these properties.

Copper is ductile, conducts electricity well, and is usually not magnetic.

Answer: The material could be copper.

Important Things to Remember

• Physical properties can be observed or tested without changing the material into something new.
• Malleability is the ability to be shaped by pressing or hammering.
• Ductility is the ability to be pulled into wire.
• Thermal conductivity tells how well heat moves through a material.
• Electrical conductivity tells how well electricity moves through a material.
• Magnetism tells whether a material is attracted to a magnet.
• Scientists often use several tests to classify a material.

Brief Summary

Physical properties help us describe, test, and sort materials. By studying malleability, ductility, thermal conductivity, electrical conductivity, and magnetism, we can learn why different materials are useful for different jobs.

When scientists test these properties, they are learning about the material without changing it into a new substance. That is what makes these properties physical properties.

Density and Buoyancy

Have you ever dropped a toy in water and watched what happened? Some things float on top of the water. Some things sink to the bottom. This lesson will help you learn why.

We can think about this with two big ideas: density and buoyancy. Those are big words, but the ideas are simple.

Density means how much “stuff” is packed into something. If something has a lot of stuff packed into a small space, it is more dense. If something has less stuff packed into the same space, it is less dense.

Buoyancy is the push that water gives to things. Water pushes up on objects. That push can help an object float.

When an object is placed in water, two things matter:

• How heavy the object is for its size
• How much water pushes up on it

If the water’s push up is strong enough, the object floats. If the object is too heavy for its size, it sinks.

Easy way to remember:

• Float = stays on top or near the top of water
• Sink = goes down in water

Let’s compare some everyday objects.

• A cork often floats.
• A rock usually sinks.
• A rubber duck floats.
• A metal spoon usually sinks.

Why? A cork and a duck are not packed as tightly with matter as a rock or a spoon. Water can push them up enough to help them float.

Water pushes up

When you put something in water, it moves some water out of the way. The water then pushes back up on the object. This is buoyancy.

If an object pushes water away and gets a big enough upward push, it can float. If it does not get enough push, it sinks.

Shape matters too

Shape can help an object float. A wide shape can spread out and push more water away. That can help water push up more.

This is why a big boat can float, even though it is made of metal. The boat’s shape helps it push aside lots of water.

A small metal coin sinks, but a large boat made of metal can float. The shape changes what happens.

Air can help things float

Some objects have air inside them. Air makes the whole object less packed with matter. That can help it float.

An empty plastic bottle may float because there is air inside. If it fills with water, it may sink lower or sink all the way.

We can test float or sink

You can make a prediction before placing an object in water. A prediction is a smart guess.

1. Look at the object.
2. Think: Is it light for its size, or heavy for its size?
3. Think about its shape.
4. Predict: Will it float or sink?
5. Test it in water.

Worked Example 1

Question: A leaf falls into a pond. Will it float or sink?

Think: A leaf is very light for its size. It is not packed tightly with matter.

Answer: The leaf will most likely float.

Worked Example 2

Question: A rock is dropped into water. Will it float or sink?

Think: A rock is heavy for its size. It is packed tightly with matter.

Answer: The rock will sink.

Worked Example 3

Question: You put an empty plastic bottle in water. Then you put a bottle full of water in water. What may happen?

Think: The empty bottle has air inside, which helps it float. The full bottle has more water inside, so it is heavier.

Answer: The empty bottle will likely float higher. The full bottle may sink lower or even sink.

Worked Example 4

Question: A ball of clay sinks. If you shape the clay like a little bowl, what might happen?

Think: Changing the shape can help the clay push more water away. The bowl shape can trap air too.

Answer: The clay bowl might float, even though the clay ball sank.

Let’s notice patterns

• Objects that are heavy for their size often sink.
• Objects that are light for their size often float.
• Objects with shapes that push more water away can float better.
• Objects with air inside often float more easily.

Float and sink words

• Float: stay on top of water
• Sink: go to the bottom
• Dense: packed with a lot of matter
• Buoyancy: the push up from water

Try thinking about these

• Why does a wooden block float? Because it is less dense than water.
• Why does a pebble sink? Because it is more dense than water.
• Why can a boat float? Because its shape helps water push up on it.

Sometimes we compare using simple ideas like “more” and “less.”

If an object has more packed stuff in the same space, it is more dense.

If an object has less packed stuff in the same space, it is less dense.

We can show the idea in a very simple way:

More packed stuff \(\rightarrow\) more dense

Less packed stuff \(\rightarrow\) less dense

And for water:

If water pushes up enough \(\rightarrow\) float

If water does not push up enough \(\rightarrow\) sink

Important idea: Not all heavy things sink, and not all light things float. Shape matters too. A heavy boat can float because it is shaped in a way that helps it push aside lots of water.

Mini review

• Density is how packed something is.
• Buoyancy is water pushing up.
• Things float when the push up from water is enough.
• Things sink when the push up is not enough.
• Shape and air inside can help something float.

Summary

Objects float or sink because of density and buoyancy. Density tells us how packed an object is. Buoyancy is the upward push from water. Objects that are less dense than water often float, and objects that are more dense than water often sink. Shape also matters, which is why boats can float.

Homogeneous and Heterogeneous Mixtures

Everything around us is made of matter. Matter is anything that takes up space and has mass. Many kinds of matter are not just one material by themselves. Instead, they are mixtures.

A mixture is made when two or more kinds of matter are put together, but they do not turn into a brand-new substance. Each part keeps its own properties. For example, if you mix cereal and raisins, you still have cereal and raisins.

Scientists sort mixtures into two main groups: homogeneous mixtures and heterogeneous mixtures. Learning the difference helps us describe what matter looks like and how it behaves.

What Is a Homogeneous Mixture?

A homogeneous mixture is a mixture that looks the same all the way through. The parts are spread out evenly, so you cannot easily see the different materials.

Another name for many homogeneous mixtures is a solution. In a solution, one material dissolves into another. For example, when salt dissolves in water, the salt spreads out so evenly that the mixture looks like plain water.

Homogeneous mixtures have a uniform composition. That means each small sample is like every other small sample. If you taste a glass of lemonade that is well mixed, the top and bottom should taste about the same.

• Looks the same throughout
• Parts are evenly mixed
• Different materials are hard or impossible to see
• Often called a solution

Examples of Homogeneous Mixtures

• Salt water
• Sugar water
• Air
• Lemonade with the sugar fully dissolved

What Is a Heterogeneous Mixture?

A heterogeneous mixture is a mixture that does not look the same all the way through. You can often see different parts, layers, or pieces.

In a heterogeneous mixture, the materials are not evenly spread out. One spoonful or handful may be different from another spoonful or handful.

For example, in a trail mix, you can see peanuts, raisins, and chocolate pieces. They are all mixed together, but each part is still easy to notice.

• Does not look the same throughout
• Parts are not evenly mixed
• Different materials can often be seen
• May have layers or chunks

Examples of Heterogeneous Mixtures

• Salad
• Trail mix
• Sand and water
• Oil and water

How to Tell the Difference

Here are some simple questions you can ask when you look at a mixture:

1. Does it look the same everywhere?
   If yes, it may be homogeneous.
2. Can I see different parts?
   If yes, it may be heterogeneous.
3. Are the materials spread out evenly?
   If yes, it is likely homogeneous.
4. Do some parts have more of one material than others?
   If yes, it is likely heterogeneous.

Important Idea: “Too Small to See”

Sometimes a homogeneous mixture may look like only one thing, but it is still made of more than one kind of matter. The particles are just spread out so evenly that your eyes cannot see the separate parts.

For example, in salt water, the salt seems to disappear. It does not really vanish. It breaks into tiny particles and spreads through the water.

Worked Example 1: Salt Water

Question: A student stirs salt into a cup of water until all the salt dissolves. Is this homogeneous or heterogeneous?

Step 1: Ask, “Can I see the salt?” No, not after it dissolves.

Step 2: Ask, “Does the mixture look the same all the way through?” Yes.

Answer: This is a homogeneous mixture.

Why? The salt is spread evenly through the water.

Worked Example 2: Cereal in Milk

Question: Is a bowl of cereal in milk homogeneous or heterogeneous?

Step 1: Look at the mixture. Can you see different parts? Yes, you can see cereal and milk.

Step 2: Does it look the same throughout? No.

Answer: This is a heterogeneous mixture.

Why? The cereal pieces are separate from the milk and easy to see.

Worked Example 3: Lemonade

Question: A pitcher of lemonade has water, lemon juice, and sugar. The sugar is fully dissolved, and there are no lemon pieces floating in it. Is it homogeneous or heterogeneous?

Step 1: Check whether the mixture looks the same from top to bottom. Yes, it does.

Step 2: Check whether you can see the separate parts. No, you cannot.

Answer: This is a homogeneous mixture.

Why? The ingredients are mixed evenly, so the lemonade has a uniform look.

Worked Example 4: Sand and Water

Question: A jar has sand mixed into water. After a short time, the sand settles at the bottom. Is it homogeneous or heterogeneous?

Step 1: Look for visible parts. You can see the sand and the water.

Step 2: Ask if the mixture is the same throughout. No. The bottom has more sand than the top.

Answer: This is a heterogeneous mixture.

Why? The materials are not evenly mixed and can be seen separately.

Homogeneous or Heterogeneous? Quick Practice

• Air → homogeneous
• Fruit salad → heterogeneous
• Sugar dissolved in tea → homogeneous
• Pizza → heterogeneous
• Oil and vinegar dressing → heterogeneous

A Helpful Memory Trick

You can remember it like this:

• Homo sounds like “same” → homogeneous means it looks the same throughout.
• Hetero means “different” → heterogeneous means different parts can be seen.

Why This Matters in Science

Describing mixtures helps scientists observe and compare matter. It also helps people in everyday life. When you cook, clean, or make a drink, you are often making mixtures.

If you know whether a mixture is homogeneous or heterogeneous, you can better understand how it looks, how it might separate, and how evenly its materials are spread out.

Summary

A mixture is made of two or more kinds of matter put together. In a homogeneous mixture, the materials are evenly mixed and the mixture looks the same throughout. In a heterogeneous mixture, the materials are not evenly mixed, and you can often see different parts. When deciding which type a mixture is, ask: Does it look the same everywhere, or can I see different parts?

Solutions, Solutes, and Solvents

Have you ever stirred sugar into tea or mixed drink powder into water? When the substance seems to “disappear,” it has not vanished. It has mixed evenly into the liquid. This kind of mixture is called a solution.

In this lesson, you will learn what a solution is, what the solute and solvent are, and how the amount of solute changes the concentration of a solution. You will also see how concentration can affect what we observe, such as color, taste, and how much more can dissolve.

What is a solution?

A solution is a mixture in which one substance is spread out evenly through another substance. In a solution, the parts are mixed so well that you usually cannot see the different parts anymore.

Solutions are a kind of matter because they take up space and have mass. Many solutions are liquids, but solutions can be made in other ways too. In 5th grade science, the most common examples use a liquid.

The two main parts of a solution

• Solute: the substance that gets dissolved.
• Solvent: the substance that does the dissolving.

If you mix salt into water, the salt is the solute and the water is the solvent. The salt spreads evenly through the water and makes a saltwater solution.

A helpful way to remember this is: solute = gets dissolved, and solvent = does the dissolving.

What does “dissolve” mean?

To dissolve means to mix a substance into another substance so evenly that it seems to disappear. The solute is still there, even if you cannot see it.

For example, when sugar dissolves in water, the sugar is still in the water. You can prove it by tasting the water. It will taste sweet.

Common examples of solutions

• Sugar water
• Saltwater
• Lemonade mix in water
• Hot cocoa mix in milk or water

In each example, one substance dissolves into another and forms a solution.

How can you tell which part is the solute and which part is the solvent?

Ask yourself these questions:

1. What substance is being added?
2. What substance is doing the dissolving?
3. Which substance is there in the larger amount most of the time?

Usually, the solute is the part added in a smaller amount, and the solvent is the part in a larger amount. For example, in chocolate milk, the chocolate powder or syrup is the solute, and the milk is the solvent.

Concentration: how much solute is in the solution

Concentration tells us how much solute is mixed into a certain amount of solvent or solution.

If a solution has only a little solute, it is dilute. If it has a lot of solute, it is concentrated.

• Dilute solution: less solute mixed in
• Concentrated solution: more solute mixed in

Imagine two cups of water. If you put 1 spoonful of drink mix into the first cup and 3 spoonfuls into the second cup, the second cup is more concentrated.

How concentration changes what we notice

Changing concentration can change the physical properties we observe. Physical properties are things we can notice with our senses or measure without making a new substance.

When concentration changes, you may notice:

• Color: a more concentrated drink mix may look darker.
• Taste: a more concentrated sugar solution may taste sweeter.
• Smell: a more concentrated flavored solution may smell stronger.

The substances are still the same substances, but the mixture may look or taste different because the amount of solute changed.

Can all of the solute always dissolve?

No. A solvent can dissolve only a certain amount of solute at a time. If you keep adding more solute, eventually some may stop dissolving and settle at the bottom.

For example, if you keep adding sugar to water and stirring, there may come a point when extra sugar stays at the bottom. That means the water cannot dissolve any more sugar at that moment.

Things that can help a solute dissolve faster

• Stirring the mixture
• Heating the solvent, in many cases
• Breaking the solute into smaller pieces

These things can help the solute dissolve faster, but they do not change which substance is the solute or which is the solvent.

Worked Example 1: Identify the parts

You stir 2 spoonfuls of sugar into a glass of water.

Step 1: What is being dissolved? The sugar.

Step 2: What is doing the dissolving? The water.

Answer: Sugar = solute, water = solvent, and together they make a solution.

Worked Example 2: Compare concentration

Cup A has 1 spoonful of salt in 1 cup of water. Cup B has 3 spoonfuls of salt in 1 cup of water.

Both cups have the same amount of water, but Cup B has more solute.

Answer: Cup B is the more concentrated solution.

Worked Example 3: Same solute, different amounts of solvent

Jar 1 has 2 spoonfuls of lemonade powder in 1 cup of water. Jar 2 has 2 spoonfuls of lemonade powder in 3 cups of water.

Both jars have the same amount of solute, but Jar 2 has more solvent.

That means the solute is spread out more in Jar 2.

Answer: Jar 1 is more concentrated, and Jar 2 is more dilute.

Worked Example 4: What if some does not dissolve?

A student adds spoonful after spoonful of cocoa mix to milk. After stirring, some powder remains at the bottom.

This shows that not all of the solute dissolved.

Answer: The cocoa mix is the solute, the milk is the solvent, and the extra powder at the bottom means the solvent could not dissolve all of the solute.

Important ideas to remember

• A solution is a mixture that looks evenly mixed.
• The solute is the part that gets dissolved.
• The solvent is the part that does the dissolving.
• Concentration tells how much solute is in the solution.
• More solute in the same amount of solvent makes a solution more concentrated.
• Less solute in the same amount of solvent makes a solution more dilute.

Quick check

1. In saltwater, which is the solute and which is the solvent?
2. If two cups have the same amount of water, which one is more concentrated: the cup with 1 spoonful of sugar or the cup with 4 spoonfuls of sugar?
3. If powder stays at the bottom after stirring, what does that tell you?

Summary

A solution is a mixture in which one substance dissolves evenly into another. The substance being dissolved is the solute, and the substance doing the dissolving is the solvent. Concentration tells how much solute is in a solution. When concentration changes, the solution may look darker, taste stronger, or smell stronger.

Mixtures and Solutions

Everything around us is made of matter. Matter is anything that takes up space. Sometimes we put different kinds of matter together. When we do that, we can make a mixture or a solution.

In this lesson, we will learn what mixtures and solutions are, how they are alike, and how they are different. We will also learn that some things can be taken apart again.

What is a mixture?

A mixture is made when two or more things are put together, but they do not turn into something new. Each part is still there.

In a mixture, you can often see the different parts. You may be able to pick them apart with your hands, a spoon, or a strainer.

• Trail mix is a mixture of nuts, cereal, and raisins.
• A bowl of toy blocks with different colors is a mixture.
• Sand and small rocks together make a mixture.

What is a solution?

A solution is a special kind of mixture. It happens when one material mixes into a liquid so well that you cannot see it anymore.

When something seems to disappear in a liquid, we say it dissolves. The solid is still there, but it is spread out in the liquid.

• Sugar in water can make a solution.
• Salt in water can make a solution.
• Drink powder in water can make a solution.

Mixture or solution?

Both mixtures and solutions are made by putting things together. But there is an important difference.

• In a mixture, you can often see the parts.
• In a solution, one part dissolves in a liquid, so you cannot see it.

Let us look at it another way:

• Cereal and milk is usually a mixture because you can still see the cereal.
• Sugar water is a solution because the sugar dissolves.

Can mixtures be separated?

Yes. Many mixtures can be separated. That means we can take the parts apart again.

We can separate mixtures in simple ways:

• Pick pieces apart by hand.
• Use a spoon.
• Use a strainer to let small pieces pass through and keep big pieces out.
• Sort by color, size, or shape.

For example, if buttons and beads are mixed together, you can sort them into groups. If sand and larger rocks are mixed together, you can use a screen or strainer.

Can solutions be separated?

A solution is harder to separate because the dissolved material is spread through the liquid.

For example, if salt dissolves in water, you cannot pick the salt out with your fingers. The salt is still in the water, but it is too mixed in to see.

What dissolves?

Some solids dissolve in liquids, and some do not.

• Sugar can dissolve in water.
• Salt can dissolve in water.
• Sand does not dissolve in water.
• Small rocks do not dissolve in water.

If something does not dissolve, it may sink, float, or stay in pieces. Then it is not a solution.

How can we tell what kind of combination it is?

Ask these easy questions:

1. Did I put two or more things together?
2. Can I still see the parts?
3. Did one part dissolve in a liquid?

If you can still see the parts, it is probably a mixture.

If one part dissolved in the liquid and you cannot see it, it is probably a solution.

Worked Example 1

You have a bowl with raisins and cereal.

Question: Is it a mixture or a solution?

Step 1: Look to see if you can still see the parts.

Yes. You can see the raisins. You can see the cereal.

Step 2: Ask if anything dissolved.

No. Nothing dissolved.

Answer: It is a mixture.

Worked Example 2

You stir sugar into a cup of water. After stirring, you cannot see the sugar.

Question: Is it a mixture or a solution?

Step 1: Ask if the sugar is still easy to see.

No. You cannot see it.

Step 2: Ask if the sugar dissolved in the water.

Yes. It dissolved.

Answer: It is a solution.

Worked Example 3

You pour sand into water. The sand falls to the bottom. You can still see the sand.

Question: Is it a mixture or a solution?

Step 1: Can you still see the sand?

Yes.

Step 2: Did the sand dissolve?

No.

Answer: It is a mixture, not a solution.

Worked Example 4

You have a bucket with large rocks and small rocks.

Question: How can you separate the mixture?

Step 1: Look at how the parts are different.

Some rocks are big. Some rocks are small.

Step 2: Choose a way to separate them.

You can sort them by size with your hands. You could also use a screen that lets small rocks go through.

Answer: This mixture can be separated by size.

Things to remember

• A mixture is two or more things together.
• In a mixture, you can often see the parts.
• A solution is when something dissolves in a liquid.
• In a solution, you may not be able to see the part that dissolved.
• Many mixtures can be separated.
• Some solids dissolve in water, and some do not.

Let’s practice thinking

• Peanuts and pretzels in one bowl: mixture
• Salt stirred into water: solution
• Sand and water: mixture
• Red and blue buttons in a box: mixture

Summary

When we put materials together, we can make mixtures and solutions. In a mixture, the parts usually stay easy to see. In a solution, one material dissolves in a liquid and seems to disappear. Knowing whether something is a mixture or a solution helps us understand how matter can change and how some materials can be separated.

Separation Techniques for Mixtures

Sometimes materials get mixed together. A mixture is when two or more things are together, but they are not changed into something new.

For example, sand and water make a mixture. So do iron nails and cereal, or salt mixed into water. The things in a mixture can often be separated again.

Scientists use different ways to separate mixtures. In this lesson, we will learn about filtration, evaporation, magnetic extraction, and chromatography.

Why do we separate mixtures?

We separate mixtures when we want to collect one part, clean something, or learn what is inside the mixture.

• To get clean water from water with dirt in it
• To remove metal pieces from other objects
• To get salt back from salt water
• To see the different colors inside ink

1. Filtration

Filtration is a way to separate a solid from a liquid by using a filter. A filter has tiny holes. The liquid can pass through, but bigger solid pieces get trapped.

Think about pouring muddy water through a coffee filter. The water goes through. The dirt stays behind.

Filtration works best when:

• One part is a liquid
• The other part is a solid that does not dissolve
• The solid pieces are big enough to get caught by the filter

Examples of filtration:

• Separating sand from water
• Using a strainer to separate pasta from water
• Using an air filter to catch dust

2. Evaporation

Evaporation happens when a liquid changes into a gas and goes into the air. If a mixture has something dissolved in water, evaporation can help separate it.

For example, if salt is mixed into water, the salt seems to disappear. But it is still there. It is just dissolved. If the water evaporates, the salt is left behind.

Evaporation works best when:

• A solid is dissolved in a liquid
• The liquid can dry up or turn into gas
• You want to keep the solid part

Examples of evaporation:

• Getting salt from ocean water
• A puddle drying after rain
• Sugar crystals forming after water leaves a mixture

3. Magnetic Extraction

Magnetic extraction means using a magnet to pull out magnetic materials from a mixture.

Not every metal sticks to a magnet. But some metals, like iron, do. If a mixture has iron in it, a magnet can help separate it from the other parts.

Magnetic extraction works best when:

• One part of the mixture is magnetic
• The other parts are not magnetic

Examples of magnetic extraction:

• Picking up iron filings from sand
• Removing metal scraps from a pile of trash
• Finding paper clips mixed with buttons

4. Chromatography

Chromatography is a way to separate colors or liquids in a mixture. A common kind uses paper and a little water.

If you draw a dot with a marker on paper and dip the bottom of the paper in water, the water moves up the paper. As it moves, it can carry the colors in the ink. Some colors move farther than others, so the colors spread apart.

Chromatography helps us see that one color of ink may really be made of many colors.

Chromatography works best when:

• The mixture has colors or liquids that travel at different speeds
• You want to see the parts of the mixture spread out

Examples of chromatography:

• Separating the colors in black marker ink
• Comparing different pens
• Seeing hidden colors in food coloring

How do we choose the right separation method?

We look at the properties of the materials in the mixture. Properties are things we can notice or test, like size, whether something dissolves, whether it is magnetic, or how it moves with water.

• If a solid is too big to pass through a filter, use filtration.
• If a solid is dissolved in water, use evaporation.
• If one part is magnetic, use magnetic extraction.
• If colors in ink can spread apart on paper, use chromatography.

Worked Example 1: Sand and Water

Problem: Mia has a cup of sand mixed with water. How can she separate them?

Think: Sand does not dissolve in water. The sand pieces are solid and can be trapped by a filter.

Answer: Mia should use filtration.

Steps:

1. Put a filter or paper towel over a cup.
2. Pour the sand and water mixture slowly.
3. The water goes through.
4. The sand stays on the filter.

Worked Example 2: Salt Water

Problem: Leo wants to get the salt back after it was mixed into water. What should he do?

Think: The salt is dissolved, so a filter will not catch it. If the water leaves, the salt will stay behind.

Answer: Leo should use evaporation.

Steps:

1. Put the salt water in a shallow dish.
2. Wait for the water to evaporate.
3. The water goes into the air.
4. The salt is left in the dish.

Worked Example 3: Paper Clips and Plastic Beads

Problem: A box has paper clips mixed with plastic beads. How can they be separated?

Think: Paper clips are metal and can be magnetic. Plastic beads are not magnetic.

Answer: Use magnetic extraction.

Steps:

1. Move a magnet over the mixture.
2. The paper clips stick to the magnet.
3. The plastic beads stay behind.
4. Pull away the magnet with the paper clips.

Worked Example 4: Black Marker Ink

Problem: Ava wants to know if black marker ink is really just one color. What can she do?

Think: Some inks are made from many colors. Paper chromatography can spread the colors apart.

Answer: Ava should use chromatography.

Steps:

1. Draw a small dot of black ink near the bottom of a strip of paper.
2. Put only the bottom edge of the paper in water.
3. Watch the water move up the paper.
4. See if the black ink separates into different colors.

Let’s Compare the Methods

• Filtration: separates a solid from a liquid when the solid does not dissolve
• Evaporation: separates a dissolved solid from a liquid
• Magnetic extraction: separates magnetic parts from non-magnetic parts
• Chromatography: separates colors or liquids that move differently

Helpful Clues

Ask these questions when you see a mixture:

• Is one part a solid and one part a liquid?
• Does the solid dissolve or not?
• Does a magnet attract one part?
• Are there colors that might spread apart on paper?

Things to Remember

• A mixture is made of parts that are together but not changed into something new.
• Different mixtures need different separation methods.
• The best method depends on the properties of the materials.
• Scientists observe carefully before choosing a method.

Summary

Mixtures can often be separated because each part keeps its own properties. We can use filtration to trap solids, evaporation to leave dissolved solids behind, magnetic extraction to pull out magnetic materials, and chromatography to spread colors apart. When we know the properties of a mixture, we can choose the best way to separate it.

Density and Buoyancy

Everything around us is made of matter. Matter takes up space and has mass. A rock, a spoon, water, and even a rubber duck are all matter.

Sometimes objects float in water, and sometimes they sink. Why does that happen? Two big ideas help us understand this: density and buoyancy.

Density means how closely packed the matter is inside something. If the tiny pieces of matter are packed very tightly, the object has high density. If the tiny pieces are more spread out, the object has low density.

You can think of it like two same-size boxes. One box is filled tightly with books. The other box is filled with cotton balls. They are the same size, but the box with books is much heavier because more matter is packed inside. That is like higher density.

Buoyancy is the upward push from a liquid, like water. Water pushes up on objects that are in it. This push helps some objects float.

An object will usually float if it is less dense than the liquid. An object will usually sink if it is more dense than the liquid.

For 3rd Grade, we can remember it this way:

• Less dense than water = usually floats
• More dense than water = usually sinks

Water is a liquid, so we often test buoyancy by putting things in water. But other liquids can be different too. Something might sink in one liquid and float in another.

Main Idea 1: Size does not always tell us if something will sink or float.

A tiny pebble sinks, but a big beach ball floats. The pebble is smaller, but its matter is packed more tightly. The beach ball has air inside, so overall it is less dense.

Main Idea 2: Shape can matter too.

A ball of clay may sink, but the same clay shaped like a bowl or boat may float for a while. That happens because the new shape spreads out the matter and traps air, which lowers the overall density of the object.

Main Idea 3: Air can help something float.

Many floating objects have air inside them. A life jacket, pool noodle, and inflatable ball float because they have trapped air. The air helps make the whole object less dense than water.

Main Idea 4: Heavy does not always mean sink.

A huge ship can float, even though it is very heavy. A small metal coin can sink, even though it is light in your hand. What matters is how much matter is packed into the space and how the water pushes up on it.

Let’s connect this to particles.

All matter is made of tiny particles. In some materials, the particles are packed closely together. In others, they are not packed as tightly. When particles are packed more closely, the material is usually denser.

That is why a rock often sinks in water. Its particles are packed tightly. Wood often floats because its particles are usually less packed than the particles in rock.

Worked Example 1: Rock or Wood?

You place a small rock and a piece of wood into water.

1. The rock has tightly packed matter.
2. The wood has less tightly packed matter.
3. The rock is more dense than water, so it sinks.
4. The wood is less dense than water, so it floats.

Answer: The rock sinks, and the wood floats.

Worked Example 2: Big Beach Ball or Small Marble?

A big beach ball and a small marble are placed in water. Which one floats?

1. The beach ball is big, but it is filled with air.
2. The marble is small, but glass is packed tightly.
3. The beach ball is less dense than water.
4. The marble is more dense than water.

Answer: The beach ball floats, and the marble sinks.

This shows us that bigger does not always mean sink and smaller does not always mean float.

Worked Example 3: Clay Ball and Clay Boat

You have the same amount of clay. First, you roll it into a tight ball. Then you reshape it into a little boat.

1. The clay ball has matter packed into a small space.
2. It is more dense overall, so it sinks.
3. The clay boat shape spreads the clay out.
4. It also holds air and lets water push up on more of it.
5. The clay boat may float.

Answer: The clay ball sinks, but the clay boat can float.

Worked Example 4: Predict and Explain

A plastic bottle with the cap on is placed in water. Then the same bottle is filled with sand and placed in water. What happens?

1. The empty bottle has lots of air inside.
2. This makes the bottle less dense overall, so it floats.
3. When the bottle is filled with sand, more matter is packed inside.
4. The bottle becomes more dense.
5. It may sink.

Answer: The empty bottle floats. The sand-filled bottle is more likely to sink.

How can we test buoyancy?

We can make a simple prediction and test it.

• Pick an object.
• Ask: Do I think it will float or sink?
• Put it gently in water.
• Observe what happens.
• Explain why using density and buoyancy.

Here are some sentence starters you can use:

• I predict ___ will float because ___.
• I predict ___ will sink because ___.
• It floated because it was less dense than water.
• It sank because it was more dense than water.

Things that often float:

• Wood
• Rubber duck
• Beach ball
• Empty plastic bottle
• Foam

Things that often sink:

• Rock
• Metal spoon
• Coin
• Marble

Be careful: these are common examples, but not every object made of the same material acts exactly the same. Shape, trapped air, and what is inside the object can change whether it floats or sinks.

A tiny math idea: If two objects are the same size, the one with more matter packed inside is denser.

We can compare like this:

If object A and object B are the same size, and object A has more mass, then:

You do not need to calculate density yet. Just remember: more packed = more dense.

Quick Check

1. What does density mean?
   Answer: It means how closely packed the matter is inside something.
2. What is buoyancy?
   Answer: It is the upward push from a liquid.
3. If an object is less dense than water, what will it usually do?
   Answer: It will float.
4. If an object is more dense than water, what will it usually do?
   Answer: It will sink.

Summary

Density tells us how tightly matter is packed. Buoyancy is the upward push from water or another liquid. Objects that are less dense than water usually float, and objects that are more dense than water usually sink.

Remember: size alone does not decide if something sinks or floats. Shape, trapped air, and how packed the particles are all help explain buoyancy.