requires spectroscopic, magnetic or structural data. when the bond order has to be ascertained along with an isolated tandem of a heteronuclear and a homonuclear bond. An example is thiosulfate having two possible oxidation states (bond orders are in blue and formal charges in green): The S–S distance measurement in thiosulfate is needed to reveal that this bond order is very close to 1, as in the formula on the left. Ambiguous/arbitrary oxidation states when the electronegativity difference between two bonded atoms is very small (as in H3PO3). Two almost equivalent pairs of oxidation states, arbitrarily chosen, are obtained for these atoms. when an electronegative p-block atom forms solely homonuclear bonds, the number of which differs from the number of two-electron bonds suggested by rules. Examples are homonuclear finite chains like (the central nitrogen connects two atoms with four two-electron bonds while only three two-electron bonds are required by 8 − N rule) or (the central iodine connects two atoms with two two-electron bonds while only one two-electron bond fulfills the 8 − N rule). A sensible approach is to distribute the ionic charge over the two outer atoms. Such a placement of charges in a polysulfide (where all inner sulfurs form two bonds, fulfilling the 8 − N rule) follows already from its Lewis structure. when the isolated tandem of a heteronuclear and a homonuclear bond leads to a bonding compromise in between two Lewis structures of limiting bond orders. An example is N2O: The typical oxidation state of nitrogen in N2O is +1, which also obtains for both nitrogens by a molecular orbital approach. The formal charges on the right comply with electronegativities, which implies an added ionic bonding contribution. Indeed, the estimated N−N and N−O bond orders are 2.76 and 1.9, respectively, approaching the formula of integer bond orders that would include the ionic contribution explicitly as a bond (in green): Conversely, formal charges against electronegativities in a Lewis structure decrease the bond order of the corresponding bond. An example is carbon monoxide with a bond-order estimate of 2.6. Fractional oxidation states 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