Particulate Nature of Matter
Heat energy decides the state
Put the chapter together and find out what decides whether matter is solid, liquid or gas.
Put the whole chapter together. Matter is made of tiny particles held by attractions. How strong those attractions are depends on the distance between the particles, and that distance depends on the particles' thermal (heat) energy. So, in the end, thermal energy decides the state of matter.
In a solid, the particles have little thermal energy. They stay close, feel strong attractions, and can only vibrate in fixed places.
At the melting point, the heat supplied is used to overcome those attractions, and the solid becomes a liquid. The particles can leave their fixed places. They move only slightly farther apart, but that small change weakens the attractions just enough to let them move around, still within a limited space.
In a gas, the particles have enough energy to overcome the attractions completely, so they move freely in all directions.
| Solid | Liquid | Gas | |
|---|---|---|---|
| space between particles | least | a little more | most |
| packing | closely packed | a little loosely packed | free |
| attraction | strongest | slightly weaker | negligible |
| movement | only vibrations in place | within a limited space | through all the space available |
The particles that make up matter are atoms and molecules. Iron is made of iron atoms; a water molecule is made of two hydrogen atoms and one oxygen atom. You'll learn about them in higher classes.
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