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


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)

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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