Editing Oxidation state (section)

=== Algorithm of summing bond orders ===
This algorithm works on Lewis structures and bond graphs of extended (non-molecular) solids:
{{blockquote|Oxidation state is obtained by summing the heteronuclear-bond orders at the atom as positive if that atom is the electropositive partner in a particular bond and as negative if not, and the atom’s formal charge (if any) is added to that sum. The same caveat as above applies.}}

==== Applied to a Lewis structure ====
An example of a Lewis structure with no formal charge,
:[[File:9oxstate.svg|frameless|240px]]
illustrates that, in this algorithm, homonuclear bonds are simply ignored (the bond orders are in blue).

Carbon monoxide exemplifies a Lewis structure with [[formal charges]]:

:[[File:10oxstate.svg|frameless|240px]]

To obtain the oxidation states, the formal charges are summed with the bond-order value taken positively at the carbon and negatively at the oxygen.

Applied to molecular ions, this algorithm considers the actual location of the formal (ionic) charge, as drawn in the Lewis structure. As an example, summing bond orders in the [[ammonium]] cation yields −4 at the nitrogen of formal charge +1, with the two numbers adding to the oxidation state of −3:

:[[File:11oxstate.svg|frameless|240px]]

The sum of oxidation states in the ion equals its charge (as it equals zero for a neutral molecule).

Also in anions, the formal (ionic) charges have to be considered when nonzero. For sulfate this is exemplified with the skeletal or Lewis structures (top), compared with the bond-order formula of all oxygens equivalent and fulfilling the octet and 8&nbsp;−&nbsp;''N'' rules (bottom):

:[[File:13oxstate.svg|frameless|450px]]

==== Applied to bond graph ====
A [[bond graph]] in [[solid-state chemistry]] is a chemical formula of an extended structure, in which direct bonding connectivities are shown. An example is the {{chem2|AuORb3}} [[perovskite]], the unit cell of which is drawn on the left and the bond graph (with added numerical values) on the right:

:[[File:14oxstate.svg|frameless|360px]]

We see that the oxygen atom bonds to the six nearest [[rubidium]] cations, each of which has 4 bonds to the [[auride]] anion. The bond graph summarizes these connectivities. The bond orders (also called [[bond valence]]s) sum up to oxidation states according to the attached sign of the bond's ionic approximation (there are no formal charges in bond graphs).

Determination of oxidation states from a bond graph can be illustrated on [[ilmenite]], {{chem2|FeTiO3}}. We may ask whether the mineral contains {{chem2|Fe(2+)}} and {{chem2|Ti(4+)}}, or {{chem2|Fe(3+)}} and {{chem2|Ti(3+)}}. Its crystal structure has each metal atom bonded to six oxygens and each of the equivalent oxygens to two [[iron]]s and two [[titanium]]s, as in the bond graph below. Experimental data show that three metal-oxygen bonds in the octahedron are short and three are long (the metals are off-center). The bond orders (valences), obtained from the bond lengths by the [[bond valence method]], sum up to 2.01 at Fe and 3.99 at Ti; which can be rounded off to oxidation states +2 and +4, respectively:

:[[File:15oxstate.svg|frameless|200px]]