States of Matter
Matter can exist as a solid, liquid, or a gas. It can also exist as plasma, but we won’t go into that here! The particle model can be used to describe how particles behave when they are in different states:
Solid
- Regularly spaced
- Touching
- Vibrate on the spot
Liquid
- Irregularly spaced
- Touching
- Slide over each other
Gas
- Irregularly spaced
- Not touching
- Move randomly within a container
Changes of State
We know H2O as ice, water, and steam. Ice is solid, water is liquid, and steam is a gas. Changes of state happen due to changes of energy, i.e. when matter gets hotter or colder.
When ice gets hotter, the particles become irregularly spaced and start to slide over each other. Ice has melted into water, which happens to the ice in your drink on a hot, summers day.
When water gets hotter, the particles spread apart from one another until they stop touching. They spread to fill the container they are in. Water has evaporated into steam, which happens when you boil a kettle.
When steam gets colder, the particles come closer together and touch one another again. This happens when your breathe onto a cold window, and find liquid condensation has appeared.
When water gets colder, the particles stop flowing over one another and become fixed in place. The water has frozen into ice, which happens when puddles freeze over on a cold, winters night.
Sometimes a gas can cool so quickly it goes straight from a gas to a solid. This is called deposition, and happens in clouds where water vapour solidifies straight into snowflakes!
If particles of a solid escape into a gas without becoming a liquid first, it is called sublimation. This is how we can get disco fog: dry ice is solid carbon dioxide that turns straight into a gas!