Naming chemical compounds

In a nutshell

Compounds are formed when atoms of different elements undergo a chemical reaction and form chemical bonds. There are five main rules when naming a compound. This lesson will go over these rules, with examples.

Rule 1

If a compound is made up of only two elements, then the compounds name will end in -ide.

Example

Lithium chloride ( $LiCl$ ) is composed of only lithium and chlorine atoms.

Rule 2

The first part of the compounds name must be the element that is furthest to the left in the periodic table.

Example

Potassium iodide ( $KI$ ) has potassium at the start of the name since potassium is in Group $1$ .

Rule 3

Compounds will end with the suffixes -ite or -ate if there are three or more elements present, and one of those elements is oxygen.

Examples

Potassium iodate ( $KIO_3$ ) is made up of potassium, iodine and oxygen atoms.

The -ite suffix can be found in compounds like sodium sulfite ( $Na_2SO_3$ ) and lithium nitrite ( $LiNO_2$ ).

Rule 4

In some instances, the name of the compound can contain prefixes which show how many atoms of a given element are present.

Prefixes

A prefix is a group of letters added to the start of an element. Prefixes are used to specify how many atoms of a given element are present in a molecule of a compound.

The table below shows some of the most common prefixes.

Prefix	Number of atoms
Mono-	$1$
Di-	$2$
Tri-	$3$
Tetra-	$4$
Penta-	$5$

Examples

A carbon monoxide molecule ( $CO$ ) is composed of one carbon atom and one oxygen atom, therefore it contains the prefix mono-.

Carbon dioxide ( $CO_2$ ) is made up of one carbon atom bonded to two oxygen atoms, therefore it contains the prefix di-.

Carbon tetrachloride ( $CCl_4$ ) has four chloride atoms in each molecule.

Rule 5

Acids composed of hydrogen and one other element will have a “hydro-“ prefix and an “-ic’ suffix.

Example

Hydrochloric acid has the suffix -ic.

Acids containing oxygen atoms can end with the suffix “-ous” or “-ic”.

Examples

Phosphoric acid and nitrous acid.