Solids, Liquids, Gases

In a solid, the particles are all touching and they are arranged in a regular pattern.

In a liquid, the particles are mostly touching but are not arranged in a regular pattern.

In a gas, the particles are very spread out from each other and there is no pattern.

A common mistake is to make liquids "halfway" between solids and gases. Liquids are much more like solids than they are like a gas.

This video explains about solid, liquids and gases and how they behave.

Physical Changes and Particles

• Solid to liquid is called melting.
• Liquid to gas is called evaporation.
• Gas to liquid is called condensation.
• Liquid to solid is called freezing.
• Solid to gas (directly without becoming liquid on the way) is called sublimation. For some strange reason, the reverse process is also called sublimation!

Physical changes do not form new substances and it is usually quite easy to reverse them.

In chemistry, we come across physical changes like melting and evaporation, diffusion etc. These help us to understand the way in which matter is constructed (the particulate nature of matter). To understand these concepts, we first need to understand about the particles that make up solids, liquids and gases.

Particles can be thought of as tiny little balls of "stuff". If you use this model, you have to be sure to understand just how small these particles are.

There are a few ways to picture this:

A thimble full of water probably contains 100000000000000000000000 water particles.

This is a huge number! Imagine a model of Britain in which every model person also had a model of Britain and each of these tiny model people also had a model of Britain with the right number of little people. If you count up all the little people from all of these models you are still less than the number of water particles we quoted.

Or imagine you were there at the start of the Earth's history and decided to count up from one at the speed of one number per second. You would still not be at our particle number today, 4.5 billion years later.

Or imagine taking a cup full of water from the sea. If you were somehow able to label "your" water particles and then put them back into the sea and stir up all the seas and oceans, the next cup full of water would contain around ten of your original particles. This shows that there are ten time more molecules in a cup of water than there are cupfulls in all the seas and oceans.

This video shows particle motion in solids, liquids and gases.