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. {| class="wikitable" |+ Examples of fractional oxidation states for carbon |- ! Oxidation state !! Example species |- | − || |- | − || |- | + || |} Finally, fractional oxidation numbers are not used in the description of red lead. is represented as lead(II,IV) oxide, showing the oxidation states of the two nonequivalent lead atoms. Elements with multiple oxidation states Most elements have more than one possible oxidation state. For example, carbon has nine possible integer oxidation states from −4 to +4: {| class="wikitable" |+ Integer oxidation states of carbon |- ! Oxidation state !! Example compound |- | −4 || |- | −3 || |- | −2 || , |- | −1 || , , |- | 0 || , |- | +1 || , |- | +2 || , |- | +3 || , |- | +4 || , |} Oxidation state in metals Many compounds with luster and electrical conductivity maintain a simple stoichiometric formula, such as the golden TiO, blue-black RuO2 or coppery ReO3, all of obvious oxidation state. Ultimately, assigning the free metallic electrons to one of the bonded atoms is