Electron accountancy

Subject classification: this is a chemistry resource.

Type classification: this is a lesson resource.

Aims

This Lesson will cover:

• Revision of electron counting methods
• The Covalent Bond Classification as an alternative method
• Simple classes of ligand and bond ambiguities
• Curly arrow conventions in complexes
• Composite ligands
• Formal oxidation state and the d-electron count
• Coordination number and ambiguities

Classes of ligand

L ligands (2e donors)

• PR₃, N₂, C₂H₄, CO, H₂, C₂H₂
• observed as neutral

X ligands (1e donors)

• H, halides, R (alkyl), Ar (aryl), COR (acyl), OR (alkoxides), NR₂
• observed as anions

Electron counting

The number of electrons donated by the metal = its group number.

Valence Number (VN) VN = number of X ligands + charge on complex

Coordination Number (CN) CN = number of atoms bonded to the metal CN = number of electron pairs added to the metal CN = number of ligands bonded to the metal

Ligand Bond Number (LBN) LBN = sum of L and X ligands