text: Fractional oxidation states are often used to represent the average oxidation state of several atoms of the same element in a structure. For example, the formula of magnetite is , implying an average oxidation state for iron of +. However, this average value may not be representative if the atoms are not equivalent. In a  crystal below , two-thirds of the cations are  and one-third are , and the formula may be more clearly represented as FeO·.
  Likewise, propane, , has been described as having a carbon oxidation state of −. Again, this is an average value since the structure of the molecule is , with the first and third carbon atoms each having an oxidation state of −3 and the central one −2.
  An example with true fractional oxidation states for equivalent atoms is potassium superoxide, . The diatomic superoxide ion  has an overall charge of −1, so each of its two equivalent oxygen atoms is assigned an oxidation state of −. This ion can be described as a resonance hybrid of two Lewis structures, where each oxygen has an oxidation state of 0 in one structure and −1 in the other.
  For the cyclopentadienyl anion , the oxidation state of C is −1 + − = −. The −1 occurs because each carbon is bonded to one hydrogen atom (a less electronegative element), and the − because the total ionic charge of −1 is divided among five equivalent carbons. Again this can be described as a resonance hybrid of five equivalent structures, each having four carbons with oxidation state −1 and one with −2.
  Finally, fractional oxidation numbers are not  used in the chemical nomenclature. For example the red lead Lead(II,IV) oxide| is represented as lead(II,IV) oxide, showing the oxidation states of the two nonequivalent lead atoms.