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The process of naming compounds allows chemists to communicate formulae in words rather than in chemical symbols. There are, however, a few rules about naming compounds which need to be known in order to write a formula in word form or translate a compound in word form into chemical symbols.

Ionic compounds

If the compound is ionic, then the name of the cation (usually metal) comes first, followed by the 'compound' name of the anion. To find the compound name of an anion, replace the end of the element's name with 'ide'.

name of cation + name of anion, suffix 'ide'

E.g. NaCl: sodium, the cation, first, followed by chlorine changed with the suffix 'ide' = sodium chloride

If the anion is polyatomic and contains oxygen, then the suffix is 'ate'.

name of cation + name of polyatomic oxygen anion, suffix 'ate'

E.g. Na2CO3: sodium, the cation, first, followed by a polyatomic group containing carbon and oxygen to form carbonate = sodium carbonate

Note:
E.g. MgO: magnesium, the cation, first, followed by oxygen changed with the suffix 'ide' because oxygen is the sole ion and not part of a polyatomic group = magnesium oxide

Sometimes if the compound contains hydrogen, the word 'hydrogen' shortens to 'bi' such as with NaHCO3, which is known as sodium hydrogen carbonate or sodium bicarbonate.

Hydrogen compounds

If the compound contains hydrogen and a metal, the metal comes first, followed by the word 'hydride', to denote the hydrogen component.

metal + hydride

E.g. NaH: sodium, the metal, first, followed by hydrogen changed with the suffix 'ide' = sodium hydride

If the compound contains hydrogen and a non-metal and does not contain water (H2O), then the hydrogen comes first, followed by the element's name replaced with the 'ide' suffix.

hydrogen + non-metal, suffix 'ide'

E.g. HF: hydrogen first, followed by fluorine changed with the suffix 'ide' = hydrogen fluoride

If the hydrogen non-metal compound dissolves in water, it starts with the 'hydro' prefix, followed by the element's name replaced with an 'ic' suffix, followed by 'acid'.

hydro(name of element, suffix 'ic') acid

E.g. HCl: hydro, then chlorine with an 'ic' suffix, then 'acid' = hydrochloric acid

Oxygen compounds

When naming ionic compounds that contain oxygen the basic rule is similar. If the compound contains hydrogen and an oxygen anion (oxyanion) and does not contain water, then hydrogen comes first, followed by the element name with the suffix 'ate'.
hydrogen + element, suffix 'ate'

E.g. HCO3: hydrogen followed by carbon with the suffix 'ate' = hydrogen carbonate

The 'ate' rule is used for the most common or the only compound made with an oxyanion. Some compounds, however, form more than one type of compound with oxygen and the amount of oxygen will affect the prefixes and suffixes used. This occurs for all oxyanions, with or without hydrogen involved.

Table 1.1: Naming more than one type of oxygen compound

Oxygen level Prefix

Element

Suffix

A little oxygen

hypo-

-ite

Some oxygen

 

-ite

More oxygen

 

-ate

A lot of oxygen

per-

-ate

 
E.g. Chlorine forms four different oxyanions named:

ClO = hypochlorite

ClO2 = chlorite

ClO3 = chlorate

ClO4 = perchlorate

The oxygen level corresponds with the relative amounts in different compounds and not necessarily the specific numbers of oxygen atoms. If an element forms just two types of oxyanion compounds, then the suffixes 'ite' and 'ate' will suffice.

If the hydrogen oxyanion compound is dissolved in water, it forms an acid using similar rules, only the 'ite' suffix changes to 'ous' and the 'ate' suffix changes to 'ic', followed by the word 'acid'.

Table 1.2: Naming more than one type of hydrogen oxyanion acid

Oxygen level Prefix Element Suffix Acid

A little oxygen

hypo-

-ous

Some oxygen

 

-ous

More oxygen

 

-ic

A lot of oxygen

per-

-ic

 
E.g. The above example with chlorine and oxygen plus hydrogen:

HClO = hypochlorous acid

HClO2 = chlorous acid

HClO3 = chloric acid

HClO4 = perchloric acid

Covalent compounds

If a compound contains two non-metals in a covalent bond, then:

  • the least electronegative element is named first

  • if the compound contains hydrogen, hydrogen is named first

  • the number of atoms of each element is indicated by a prefix

  • if the first element only has one atom the prefix is not used

  • the name of the element has the suffix 'ide'

least electronegative + number prefix, most electronegative element, suffix 'ide'

The prefixes used to number the atoms come from Greek and are as follows:

1 = mono- or mon-
2 = di-
3 = tri-
4 = tetra-
5 = penta-

6 = hexa-
7 = hepta-
8 = octa-
9 = nona-
10 = deca-

 
E.g. CO: carbon, the least electronegative atom, first, followed by the prefix 'mon' to indicate one atom of oxygen, the most electronegative atom, with the suffix 'ide' = carbon monoxide
 
CO2 carbon, the least electronegative atom, first, followed by the prefix 'di' to indicate two atoms of oxygen, the most electronegative atom, with the suffix 'ide' = carbon dioxide

H2O the prefix 'di' to indicate two atoms of hydrogen, which has naming priority, followed by 'mon' to indicate one atom of oxygen = dihydrogen monoxide

Common names

There are a number of common names that chemists like to use instead of the proper scientific names. Most common names and formulae are well-known. It is recommended that common names and formulae be written down as they are encountered so they can be memorised later.

Here are a few examples:

Common name

Proper name

Chemical formula

water

dihydrogen monoxide

H2O

baking soda

sodium hydrogen carbonate

NaHCO3

table salt

sodium chloride

NaCl

limestone

calcium carbonate

CaCO3

quartz

silicon dioxide

SiO2

 
See animation 1.

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Question 1/5

1. Dicarbon trioxide is a covalent compound of carbon and oxygen. How many carbon atoms are there in the molecule?

Five

Three

Two

Ten

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