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Oxidation States

In each atom of a pure element the number of electrons equals the number of protons. The oxidation state of a pure element is zero by definition. For an element that is bound to one or more other elements, the oxidation state is the number of protons minus the number of electrons. Three simple rules allow the calculation of the oxidation state of N in its compounds.

  • The oxidation state of oxygen is -2.
  • The oxidation state of hydrogen is +1.
  • The sum of oxidation states is zero for a neutral compound or the ionic charge for an ion.

Examples:

  • NH3. The net charge is zero and there are three H atoms (oxidation state +1). Therefore, the oxidation state of N is -3.
  • NO3-. The net charge is -1 and there are three O atoms (oxidation state -2). Therefore, the oxidation state of N is +5.

Oxidized species are those in which the oxidation state of an element is positive. For example, N2O, NO, and NO2 are all oxidized N species. Conversely, reduced species are those in which the oxidation state of an element is negative. For example, NH3 is a reduced N species.

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