* Ionic counting assumes unequal sharing of electrons in the bond. The more electronegative atom in the bond gains electron lost from the less electronegative atom.
* This method begins by calculating the number of electrons of the element, assuming an oxidation state.
:E.g. for a Fe has 6 electrons
:S has 8 electrons
* Two is added for every halide or other anionic ligand which binds to the metal through a sigma bond.
* Two is added for every lone pair bonding to the metal (e.g. each phosphine ligand can bind with a lone pair). Similarly Lewis and Bronsted acids (protons) contribute nothing.
* For unsaturated ligands such as alkenes, one electron is added for each carbon atom binding to the metal.