What are atoms and what are molecules?
Atoms are tiny particles that make up a substance, they are kind of like pieces of lego except they are so small we cannot see them at all.
Molecules are made up of two or more atoms, so atoms make molecules and molecules make cells. Cells make up our body, this means our entire body is made up of millions of tiny atoms!
States of matter
All matter exists as solids, liquids, or gases. These are the three main states of matter. Matter can change from one state to another by either using or releasing energy and is usually associated with temperature and pressure changes.
Here are some different states of matter:
Melting is when solids turn into liquid. When a solid is heated, the particles that were tightly bound together are given more energy and start to vibrate faster. They vibrate so much that their ordered structure changes and becomes a liquid structure with loosely bound particles.
The temperature at which a solid changes to a liquid is called the melting point. Each solid has its own melting point.
Freezing is when a liquid turns into a solid. When hot liquid lava erupts from a volcano, the change in temperature from underground to the surface of the other causes it to solidify or freeze, forming a solid rock called igneous rock.
Evaporation this is when a liquid turns into a gas. When we boil water for long enough it evaporates. Liquid doesn't have to boil to evaporate. Evaporation takes place before the boiling point has been reached.
Condensation is often seen on our bathroom mirrors where hot steam from the shower cools down and turns back into a liquid. Sometimes, early in the morning, plants outside are covered with small droplets of water. This water comes from the condensation of gas that was present in the air.
Sublimation happens when a solid turns straight into a gas without passing through the liquid state.
Reversible and irreversible changes
We’ve seen different ways in which matter can change. Each state has a different layout of molecules. Sometimes when matter changes it cannot go back to the original layout. This is because some changes are reversible and some are irreversible.
Reversible changes can go back to how they were before. Water can be transformed into ice and back into water again.
Irreversible changes cannot go back to the original state. If we cook an egg we cannot uncook it. This is an irreversible change.
