Oxidation Number and Nomenclature

Oxidation Number and Nomenclature

(i) When an element forms two monoatomic cations (representing different oxidation states), the two ions are distinguished by using the ending-ous and ic. The suffix – ous is used for the cation with lower oxidation state and the suffix – ic is used for the cation with higher oxidation state.

For example: Cu+ (oxidation number +1) cuprous

Cu2+ (oxidation number +2) cupric

(ii) Albert Stock proposed a new system known as Stock system. In this system, Roman numeral written in parentheses immediately after the name of the element indicates the oxidation states. For example,


Cu2OCopper (I) oxideSnO Tin (II) oxide
FeCl2Iron (II) chlorideMn2O7 Manganess (VII) oxide
K2Cr2O7 Potassium dichromate (VI)Na2CrO4Sodium chromate (VI)
V2O5Vanadium (V) oxideCuOCopper (II) oxide
SnO2Tin (IV) oxideFeCl3Iron (III) chloride

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