An oxidation number definition is a number assigned to a compound or element to show how many electrons were lost or gained. A negative number shows that electrons were gained, while a positive number shows that electrons were lost. A negative number is used for gaining electrons because electrons have a negative charge, so more electrons will make the compound more negative. If electrons were lost, then the overall result will be more positive, so the oxidation number is positive.
These oxidation rules are :
• The oxidation number of a free, neutral element is zero.
• The oxidation number of a monoatomic ion is equal to the charge of the ion.
• The oxidation number of Group IA elements is always +1.
• The oxidation number of Group IIA elements is always +2.
• Oxidation number of oxygen is typically -2.
• Oxidation number of hydrogen is typically +1.
• Oxidation number of Fluorine is ALWAYS -1.
• Oxidation number of other halogens (non-Fluorine) is typically -1 but can vary.
• The total oxidation number of a neutral compound is zero.
• The total oxidation number of elements in a polyatomic ion will sum the charge on the polyatomic ion.
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