My Science School

There are about 100 special chemicals called ‘elements’. There are substances that cannot be broken down into simpler chemicals. The gases oxygen and hydrogen are both elements, so are iron and gold. Every element is made up of tiny particles called ‘atoms’, which are much too small to see, even with a microscope. Oxygen is composed of oxygen atoms; iron is made up of iron atoms.

Atoms can join together to make ‘molecules’. A molecule of an element is formed from only one type of atom. For example, oxygen exists as a molecule of two oxygen atoms joined together.

Combining chemicals

When two different elements combine, they often make a compound which is very different from either of them. The element sodium is a shiny metal. The element chlorine is a green and poisonous gas. Sodium atoms and chlorine atoms can combine to make a very familiar compound — salt! However, we do not make the salt we eat by combining sodium and chlorine. The salt produced from sea water. In cooler countries, salt is mined from underground.

The atoms of one element may join up with the atoms of another element. When this happens, a completely different chemical is formed. For example, when two hydrogen atoms join with an oxygen atom, they make a molecule of water. Chemicals that are made by combining two or more elements are known as ‘compounds’. Water is a compound. Sugar, salt, plastics — in fact, most of the chemicals around us — are compounds. A compound usually has different characteristics to the elements from which it is made.