Answer:
Solids keep their shape and cannot be compressed. Let us see if the particle model can help us understand why solids behave in this way.
In a solid, the particles are packed close to each other in fixed positions. They are locked into place, and this explains why solids have a fixed shape. Look at the following images of sodium chloride (table salt). Do you remember the formula for sodium chloride?
Macroscopic view of sodium chloride
Submicroscopic view of sodium chloride
Table salt crystals are hard and have a fixed shape.
Can you see how the chloride atoms (purple) alternate with the sodium atoms (yellow) in a fixed arrangement?
Take a good look at the picture of the particles in a solid (table salt) above. You will see that they are packed in a regular arrangement. There are very small spaces between the particles in a solid.
Particles are held together by forces of attraction. In solids, these forces are strong enough to hold the particles firmly in position.
Does that mean the particles in a solid do not move at all? No. The particles in a solid move a little bit. They vibrate in their fixed positions. The more energy the particles have, the faster and more strongly they vibrate.
Do you see how we have used the particle model of matter to explain the properties of solids that we can observe? For example, the particles in solids are closely packed and have strong forces between them explains why solids have a fixed shape and you cannot compress them.
The liquid state
An important characteristic of liquids is that they flow. They fill containers they are poured into. Liquids are also not very compressible. How can these properties be explained?
Orange juice is a liquid, which can be poured.
In the liquid state, particles do not have fixed positions. They move about freely, but they stay close together because the forces of attraction between them are quite strong, but not as strong as in solids.
Have you noticed how a liquid always takes the shape of the container it is in? Within the liquid, the particles slip and slide past each other. This is why liquid flows. Their particles are free to move around, filling the spaces left by other particles. Look at the image of the juice being poured. Let's zoom in and have a look at what the particles are doing as the juice is poured.
The particles in a liquid have small spaces between them, but not as small as in solids. The particles in a liquid are loosely arranged which means they do not have a fixed shape like solids, but they rather take the shape of the container they are in.
The speed at which the particles move around inside the liquid depends on the energy of the particles. When we heat a liquid, we are giving the particles more energy and speeding them up.
In gases, the particles move at even greater speeds.
The gaseous state
Gases spread out quickly to fill all the space available to them. Think of when you blow up a balloon. The air that you blow into the balloon fills up the whole balloon. A gas will fill the entire space that is available to it. This is because the particles in a gas have no particular arrangement.
Gases do not have a fixed shape. Think about the balloon again: the gas fills the entire space inside the balloon. You can squeeze the balloon, changing the shape.
Gases fill the space available to them.
Gases do not have a fixed shape.
Gas particles move very fast, much faster than in solids and liquids. The particles in a gas possess a lot of energy.
Have you ever tried to compress the gas in a syringe or in a bicycle pump? Why do you think you can compress the gas?
In gases, the forces between particles are very weak. This explains why the particles in gases are not neatly arranged. They are not held together tightly and there are large spaces between them. These spaces are much larger than in the solid and liquid state.
Explanation:
