Changing States of Matter

​Did you know that water is the only substance on Earth that exists as a solid (ice), liquid and gas (water vapour) at normal temperature?
At the end of this lesson, you should be able to:
  • explain the Kinetic (Particle) Theory of Matter
  • explain what happens to matter when it changes state
  • explain what is special about water.

Kinetic Theory of Matter
Sometimes known as the Particle Theory of Matter.
The Kinetic Theory of Matter can be remembered in 7 steps:
  1. All matter is made of particles
  2. Particles are always moving
  3. When heated, these particles move faster.
  4. When they are moving faster, they take up more space.
  5. When cooled, these particles move slower.
  6. When moving slower, they take up less space.
  7. All particles are held together by forces that vary in strength.
Let's try and explain that in simpler English.
  1. Solids, liquids and particles are made of atoms.
  2. Particles in solids - vibrate, liquids - roll over each other, gas - move freely
  3. Vibrate faster until they start rolling, then are free to move.
  4. For solids, we say they expand (get bigger)
  5. Cooling slows down the particles
  6. They come closer together
  7. The force between particles in solids are very strong,  between particles in liquids are not as strong, between particles in gases are weak.

​If you understand the 7 steps in the Kinetic Theory of Matter, it can help you explain many of the common things in daily life.  For example, why is there condensation on the inside of your windows in winter?  Why are there gaps on the road on bridges?  Why are some things tight in winter but loose in summer?

This knowledge is useful for the creation of new materials too.  Watch the YouTube video (use closed captions CC in English to help you understand).

Interactive  simulations  /  GAMES

Here are some links to interactive animations/games that will help you understand the states of matter and the changes in states of matter.  

Splash ABC (Australia) - Types of Matter:  Solids, Liquids, Gases

Intel Education Resources - STEM:  Changes of State

PHET - Interactive simulation:  States of Matter 
​The following needs to be downloaded.  It is safe. 

Reading to check your understanding
Chem4kids - States of Matter

Water is a little different

As you know, the water molecule (H2O) is a strange shape.  It looks like Mickey Mouse's head.  Keep this in mind.

When matter cools, the particles move closer together.  But, with the water molecule, the strange shape makes it expand (get bigger) when it cools.  

So, when you freeze water to make ice cubes, the ice cubes are bigger than the amount of water you put in.   This is also the same reason why you DO NOT put a glass bottle full of water in the freezer.  
​What will happen?