Oxidation Numbers When a covalent bond forms between two atoms with different electronegativities the shared electrons in the bond lie closer to the more electronegative atom: • The oxidation number of an atom is the charge that results when the electrons in a covalent bond are assigned to the more electronegative atom • It is the charge an atom would possess if the bonding were ionic In HCl (above) the oxidation number for the hydrogen would be +1 and that of the Cl would be -1 in oxidation numbers we write the sign first to distinguish them from ionic (electronic) charges Oxidation numbers do not refer to real charges on the atoms, except in the case of actual ionic substances. Oxidation numbers can be determined using the following rules: 1. The oxidation number for an element in its elemental form is 0 (holds true for isolated atoms and elemental substances which bond identical atoms: e.g. Cl 2 , etc) 2. The oxidation number of a monoatomic ion is the same as its charge (e.g.
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