Rules for Assigning Oxidation NumbersAs a general rule in assigning oxidation numbers, shared electrons are assumed tobelong to the more-electronegative atom in each bond. More specific rules fordetermining oxidation numbers are provided by the following guidelines.1.The atoms in a pure element have an oxidation number of zero. For example, the248atoms of pure sodium, Na, oxygen, O , phosphorus, P and sulfur, S , all haveoxidation numbers of zero.2.The more-electronegative element in a binary molecular compound is assigned thenumber equal to the negative charge it would have as an anion. The less-electronegative atom is assigned the number equal to the positive charge it wouldhave as a cation.3.Fluorine has an oxidation number of -1 in all of its compounds because it is themost electronegative element.4.Oxygen has an oxidation number of -2 in almost all compounds. Exceptions include22when it is in peroxides, such as H O , in which its oxidation number is -1, and when
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