The "ous-ic" system

Another system of naming compounds, where the first element may have more than one valence, is the "ous-ic" system. This is the oldest system and uses Latin names for many elements. In this method, the lower valence of the first element uses the suffix "-ous" and the higher valence uses the suffix "-ic".

For example:

FeO is named ferrous oxide

-the valence of the iron is two, which is the lowest valence therefore the "ous" is used

and

Fe₂O₃ is named ferric oxide

-the valence of the iron is three which is the highest valence therefore the "ic" is used

Latin Names for Some Elements
Element Latin Name

Copper Cuprum (cuprous, cupric)

Iron Ferrum (ferrous, ferric)

Lead Plumbum (plumbous, plumbic)

Mercury Mercurum (mercurous, mercuric)

Tin Stannum (stannous, stannic)

Gold Aurum (aurous, auric)

**Latin Names for Some Elements**
Element	Latin Name
Copper	Cuprum (cuprous, cupric)
Iron	Ferrum (ferrous, ferric)
Lead	Plumbum (plumbous, plumbic)
Mercury	Mercurum (mercurous, mercuric)
Tin	Stannum (stannous, stannic)
Gold	Aurum (aurous, auric)

Try the following examples!

1. PbCl₂

2. Fe₂O₃

3. SnCl₄

4. Cu₂O

5. cupric oxide

6. plumbic bromide

7. stannous chloride

8. mercurous nitrate

9. stannic carbonate

10. ferric sulphate

11. antimonius oxide

12. manganous phosphide

You are now ready to look at the prefix method of naming compounds.

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