The atoms of the different elements can join together in chemical reactions to form compounds. For example, hydrogen and oxygen are elements. They react together to form water, a compound. There are countless different ways for the elements to join together, and millions of compounds are known.
Properties of compounds
The properties of compounds are usually very different from the properties of the elements they contain. For example, hydrogen and oxygen are both gases at room temperature, but water is a liquid.
The reaction between iron and sulphur to make iron sulphide is often used in school to study elements and compounds. Look at the animation to remind you what happens in this reaction.
The table compares the properties of iron and sulphur (the two elements), and iron sulphide (the compound).
Element
Compound
iron
sulphur
iron sulphide
colour
silvery grey
yellow
black
is it attracted to a magnet?
yes
no
no
reaction with hydrochloric acid
hydrogen formed
no reaction
smelly hydrogen sulphide formed
The atoms in a compound are chemically joined together by strong forces called bonds. You can only separate the elements in a compound using another chemical reaction. Separation methods like filtration and distillation will not do this.
Compounds form when atoms join together in new ways in chemical reactions
