Below you will find some commonly asked questions about states of matter. You may also want to explore other activities related to matter and properties of matter in Lesson Plans Ideas or Student Activities for the school program.

• What is matter and what is it made of?
• What is an element?
• What is a compound?
• What is the basic structure of an atom?
• What are the three states of matter and what's the difference between these states?
• What does 'Density' mean?
• Can substances change their state of matter?
• Can we alter the state of matter of a substance?
• Do the molecules change when the state of matter changes?
• Can molecules change?
• What are some properties of matter?

What is matter and what is it made of?

Everything in the universe is made of matter - except energy.

• Matter has volume and takes up space.
• Matter has mass - on Earth it has weight and exerts pressure on things.
• Almost all matter is made up of atoms or, when atoms hook up with other atoms, molecules.

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What is an element?

If you could cut a piece of aluminum into smaller and smaller pieces, the smallest bit that would still be aluminum is called an atom. If all atoms of something are identical, they are considered an element. There are 90 naturally occurring elements, but scientists have been able to make about 25 more, though most of these survive only briefly.

To explore all the elements, look at this Periodic Table

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What is a compound?

Atoms of different elements can combine together to form molecules. Molecules in turn can form a compound. Water is a compound molecule made of 2 Hydrogen atoms and one Oxygen atom. This ability of elements to combine gives us many, many different forms of matter.

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What is the basic structure of an atom?

Each atom is made up of many smaller parts. The nucleus is in the centre of the atom and is made up of positively charged protons, and usually the same number of neutral neutrons. Each of the elements has a unique number of protons, its 'atomic number'.
Whizzing around the nucleus are negatively charged electrons, orbiting in different layers or shells. They balance the number of protons. At most, there are seven electron shells.
Scientists have discovered, by smashing atoms to bits, that there are hundreds of other parts to an atom, but just two basic kinds, quarks and leptons.

Atomic structure

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What are the three states of matter and what's the difference between these states?

All matter on Earth is usually found in one of the three states, solid, liquid or gas. Solids have a definite shape and volume.

Liquids have volume but they assume the shape of the part of the container they occupy.

Gases assume both the volume and the shape of the container. Air has no container but it is held down by gravity.

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What does 'Density' mean?

Density is a measure of the amount of matter in a given amount of space - how tightly packed the molecules are. Gases are less dense than liquids, and liquids are usually less dense than solids, but not always—think of mercury . Solids can vary a lot in density. Some can even float on liquids (ice, wood) or gases (dust).

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Can substances change their state of matter?

Solids can melt, liquids can evaporate or freeze, gases can condense into a liquid or even be cooled or pressurized to become a solid.

In a solid, atoms or molecules are in close contact.
Most solids melt to form liquid and take up more volume when they melt. An exception is water which takes up more space when it freezes as ice.
In a liquid, the atoms or molecules are usually separated by greater distances than in a solid. Movement of these atoms or molecules gives a liquid its most distinctive property - the ability to flow.
Gases are a form of matter in which the molecules are much farther apart than in either solids or liquids. The molecules vibrate in place, and dart and move around in all directions. They are so far apart they never bump into other molecules. They are in such violent motion that they spread and fill up any container.

See the molecules

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Can we alter the state of matter of a substance?

Yes.
We can change the state by heating the matter.

Most solids melt (candle wax), and liquids evaporate or boil (drying cloths on the line, water in a kettle). Heating solids makes the molecules move around faster, until they break free from their set positions and slide over and under surrounding molecules. When molecules are moving about like this, the substance is a liquid.
Because the molecules in a liquid are constantly in motion, they escape from the surface - evaporation. If the liquid is heated enough, it boils and the molecules escape from throughout the liquid. Every liquid has its own particular boiling point - water 100^o C.

We can change the state by cooling the matter.

The Sun's heat evaporates water, the water vapour cools as it rises, then turns to liquid - condenses - in clouds, small droplets come together, get heavier, fall to earth as rain or snow, flow into rivers and oceans.
Water in the ice cube tray turns to ice - freezes - when we put the tray in the freezer. A cold drink in the summer will collect water droplets on the outside of the glass, as the water in the air around the glass condenses.

We can change the state by changing the pressure around the matter.

There is much less pressure from the air on top of a mountain, because there is a smaller column of atmosphere above the mountain, than at sea level. Water on top of a 3000 m mountain boils at a lower temperature - 90^o C, and food will take longer to cook. What is the boiling point of water at sea level?
By increasing the pressure on a liquid you can raise its boiling point. Pressure cookers cook food faster because the temperature of the water goes above 100^o C. Astronauts floating in space have to wear pressurized space suits so their blood doesn't boil.

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Do the molecules change when the state of matter changes?

No, changes of state do not alter the molecules, only how tightly packed they are and how much they are moving around. The molecules can change back and forth repeatedly from one state to another. Changes like this are called reversible; most changes of state are reversible.

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Can molecules change?

Some changes in matter are not reversible.
They are called irreversible.
Chemical reactions change one kind of matter to another kind.

When you burn a candle, the wax around the wick melts. If you pour this wax off the candle, it will solidify and become wax again. This is a reversible reaction. But if you burn the candle long enough the wax disappears. The heated wax becomes a liquid, then a gas. This gas combines with oxygen from the air to make water vapour and carbon dioxide. This change is irreversible. The new substances cannot change back into wax. The bonds of the wax molecules have been broken apart. New bonds have formed to give two different chemicals, carbon dioxide and water. No atoms are created or destroyed or changed. Only the bonds between the atoms have changed to make new products.

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What are some properties of matter?

Properties describe a substance. Properties describe how a substance looks, feels or behaves.
Sulphur is yellow, rubber is often flexible, honey is viscous, water can be hot.
Marble is hard, fur is soft. Lead is heavy, aluminum is light.
Strawberries are sweet. Glass can be transparent.
We select materials for certain tasks depending on their special properties.

Take a look at properties of materials.

Try some hands-on activities to test your understanding of the properties of Materials.

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Go back to Matter

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