Compounds

When elements combine or join together new substances are formed. These substances are called compounds.

This is shown in the diagram below

Two elements join together to form a compound.

There are millions of different compounds and all of them have different properties. The properties of compounds are linked to the type of bonds formed within them.

Naming compounds

Naming compounds is easy if you follow these 3 simple rules.

Rule one

The element that is furthest left in the periodic table comes first, eg Sodium Chloride/Carbon dioxide

Rule two

If there are only two elements in the compound then the compounds name ends in –ide, eg A compound of copper and sulfur is called copper sulfide.

Rule three

If the compound contains three elements one of which is oxygen then the compound name will end in –ate or –ite, eg Calcium carbonate contains calcium, carbon and oxygen.

Sometimes the name of the compound gives information about the formula of that compound. Names of these compounds have prefixes that give the number of atoms of certain elements in each molecule.

PrefixNumber of atoms
Mono-One
Di-Two
Tri-Three
Tetra-Four
Penta-Five
Hexa-Six

Example – Carbon monoxide contains one carbon atom joined to one oxygen atom, so it has the formula CO.