Editing Oxidation state (section)

==== 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]]