Copy the following into your books then tackle the questions.

The molecules that make up elements can be described by how many atoms make up the molecule.

Monatomic = 1 atom

Diatomic = 2 atoms

Triatomic = 3 atoms.

Compounds that are made up of two types of atom only have a name that ends in -ide.

For example a compound made up of sodium and sulfur would be sodium sulfide.

The metal normally makes up the first part of the name and the non metal makes up the last part of the name.

For example a compound of iron and sulfur (FeS) would be iron sulfide.

If the non - metal is oxygen the compound is an oxide (CaO - calcium oxide)

If the non-metal is chlorine the compound is a sulfide. (FeS - iron sulfide)

If the non-metal is chlorine the compound would be a chloride (HCl - hydrogen chloride)

Some compounds can have different ratios of elements.

The actual name then has a prefix before the second part of the name to show how many of the atom there are in the molecule.

For example CO is carbon monoxide

and CO2 is carbon dioxide

a compond with three of the atoms has the prefix tri

Compounds that are made of three or more elements including oxygen end with the suffix ate

For example CuSO4 is copper sulfate

NaNO3 is sodium nitrate

CaCO3 is calcium carbonate

There are two common questions about formulae

How many elements are there in the formula?

This is simply how many capital letters there are.

For example MgSO4 has Mg; S and O so there are three elements.

How many atoms are there in the formula, this requires you to look at the numbers of each element in the formulae.

MgSO4 has one magnesium, one sulfur and four oxygens to give a total of 6 atoms

An exception to the rule about 2 and three atoms is in a family of compounds known as hydroxides.

NaOH is known as sodium hydroxide

Ca(OH)2 is known as calcium hydroxide