States of Matter

Lesson Plan - Get It!

Audio:

• How do you think water can be a solid block of ice, a liquid in a glass, or a floating cloud.

• Do you think the molecules change?
• Is it still H₂0 (two hydrogen and one oxygen atom per molecule)? Why or why not?

Take a look at all of the things around you. This may be better if you step outside for a moment.

• What types of things do you see and feel?
• Can you see houses, trees, or even a street?

All of those things are matter.

• Can you see water anywhere, maybe from a swimming pool, a stream, a pond, or even from a rain puddle?

That water is matter.

Now take a deep breath.

• Do you feel the air filling up your lungs?

Even though you can't see it, that air is matter, too.

• So why does matter matter?

Matter is everything around you. Matter is anything that has mass (Basically, mass is the measurement of atoms or molecules in an object) and takes up space.

The amount of space that is occupied by a specific object is measured in volume. Volume is the amount of space needed to hold matter.

Look again at the three forms of water pictured above.

• What are your thoughts now? 
• Is ice matter? 
• Is water as a liquid matter? 
• Is water as a gaseous cloud or vapor matter?

Yes, yes, and yes. Regardless of the state of matter of the water, it is still water. The molecules never change.

• Knowing what you know now, if you were asked to place all matter into three groups, how would you classify each group?

Think about the water example we just discussed.

One way you could group all matter is by its three forms, or states.

All matter you see on the earth can be grouped into three categories: solids, liquids, and gases. You can tell the difference between materials in these states by observing their shape, volume, and mass.

Shape is the easiest to observe when it comes to classifying matter. If it is in a form that cannot easily be changed, like a rock, an ice cube, a tree, or a person, it's a solid.

Liquids, on the other hand, take the shape of the container in which they are placed. For example, if you fill a glass with water, the water fits itself into the walls of the glass. If you spill the water from the glass onto the floor, where there are no walls to hold it in place, it spreads into a blob or puddle.

Gasses are completely different. Gas, like the air we breathe or steam or vapor that rises from boiling water, rises into the air with no definite shape, and usually cannot be contained.

(Unless you use something like a balloon. But even in that case — where helium gas is lighter than the combination of gasses that make up the air we breathe — it tries to escape because gas does not like to be confined by a shape.)

We stated above that matter is anything that has mass and takes up space, or volume.

Mass and volume are simple to measure with solids and even liquids. If you can put something on a scale, measure it with a ruler, or put it in a container with measurement markings, you can find your mass and volume. This is not so true when it comes to gasses, and here's why.

It comes down to the tiny little particles that are the building blocks of everything: atoms.

Atoms have either a positive or negative charge, like magnets. Some magnets attract each other, while other magnets repel each other. The attraction between particles determines whether a substance will be a solid, liquid, or gas. Some attractions are strong and some are weak.

In a solid, the attraction between the particles is so strong that they are packed so tightly they can only vibrate in place. In a liquid, the attraction is not quite as strong, and the particles are able to slide past each other. In a gas, the attraction is so weak that the particles are able to move quickly and freely in all directions.

This is why solids have a defined shape and a definite volume. A liquid has a definite volume, but not a definite shape; it takes the shape of its container. Gasses, on the other hand, have no definite shape or volume.

The state of a substance depends on its temperature and the amount of the attraction between its particles. As the temperature of a substance increases, so does the movement of its particles. This means that the hotter a substance becomes, the faster the particles move.

Let's think about water.

If we begin with ice and add heat, the ice will melt and become water. If we continue to apply heat to the water, it will eventually boil, and the water will become steam, which is a gas. So, as the particles in the ice move faster, they spread apart and allow the solid block to become a free-flowing liquid. Heat the free-flowing liquid, and eventually the particles will separate more and become a gas.

Let's take this concept a step further.

Like water, many substances can change their state.

Some solids can turn into a liquid, and some liquids can change into gases or a solid. Melting and freezing occur at different temperatures.

Melting occurs when a substance gains energy, increasing the motion of the particles. When particles lose energy, the energy is transferred to another substance due to the fact that energy is never lost. The particles with less energy slow down and freeze, while the particles to which the energy is transferred are heated and may boil or even melt. The process of a substance changing from a solid into a liquid is called melting.

Freezing occurs when a substance changes from a liquid to a solid. Not all substances have the same melting point or freezing point.

When a liquid changes to a gas, we say that it is boiling. When the particles of water in a pan are heated, they move faster. As the temperature continues to increase, the particles break free and become a gas. If you continue heating a substance, the particles will continue to move farther and farther apart, a process known as evaporation.

The difference between evaporation and boiling is that at the boiling point, particles throughout the liquid have enough energy to escape. With evaporation, only those particles at the surface have enough energy to break free and change into a gas. Evaporated particles are called vapor. When particles that have evaporated slow down, they can return to a liquid state. This process is called condensation.

Because the substance does not change the structure of its molecules during these processes, we call them physical changes. Only the physical state of the matter in question is changing. There are processes that do change the molecules, but we can get to those in another lesson.

Just make sure you know there are three states of matter, and sometimes a substance can change between these states without changing its molecules. Water is always water, no matter if it's a solid, a liquid, or a gas.

Ok, let's put all this new information to good use!