Characteristics of solids, liquids and gases

Lina and Leon are having breakfast. I cut you some cheese, Lina! The smelly one? Bleeh, no thank you! Then I’ll eat it all myself!

Ooops! Oh, no, Leon! You spilled milk everywhere! Let's pause here for a second and observe the scene. Cheese is made from milk, but Leon can cut it into slices and it doesn’t spill like milk.

Lina can also smell the cheese. The smell from the cheese on the other side of the table must somehow reach her nose… Just like everything around us, Lina and Leon’s breakfast is made of matter — tiny particles called atoms and molecules. These particles can be arranged in different ways. Let’s take a look at the cheese first. This block of cheese has a fixed shape.

When Leon cuts a slice, the slice keeps its shape as well. The cheese also takes up only a certain amount of space - it has a fixed volume. These are characteristics of one of the basic states of matter - a solid. Particles in solids are packed very tightly together. They form fixed structures, held by forces between atoms and molecules.

The particles are locked in their positions in these structures. The particles can’t move around freely, but they can vibrate slightly. Some other examples of solids are chairs, tables, glasses, plates, pieces of toast… Milk is different. When Leon pours milk from the container into a glass, the milk takes the shape of the glass. When he spills it — he makes a mess, because the milk spreads all over the surface.

But if he could collect all of the milk and put it back into the glass, it would still have exactly the same volume as before. So, milk takes a certain amount of space — it has a fixed volume, but it doesn’t have a fixed shape. It takes the shape of the container it’s poured into. But if the container is too small, milk can’t be squeezed into it - it will move and spill over the top edge. These are characteristics of another state of matter — liquid.

Particles inside liquids are still very close together, but they don’t form fixed structures. They vibrate like in solids, but they can also move around and rotate. Yet, the distances between particles remain quite short and the particles frequently bump into each other. This allows liquids to change shape, but keep a constant volume. Other examples of liquids include water, melted butter, dishwashing detergent or blood… And what’s the deal with the smell of cheese?

Smell is actually matter too, but in yet another state — smell is a gas. Like liquids, gases have no definite shape. But gases have no definite volume either — the same amount of gas can fill a space as big as a room or as small as a matchbox. This also means that gases can be easily squeezed to take less space - they can be compressed. Particles in gases can also spread out easily and indefinitely, unless they are enclosed in a container.

This is because particles in gases can move freely in all directions and at high speeds. Some examples of substances that normally occur in a gaseous state are air, steam, or natural gas. Did you just fart, Leon?! I guess it’s a gas too, hehehe! So these are the characteristics of three basic states of matter — solids, liquids and gases.