A new approach to the formal classification of covalent compounds of the elements

A new approach to the classification of covalent compounds of the transition metals is presented. The classification introduces the concepts of valency number and ligand bond number as alternatives to the concepts of formal oxidation state and coordination number. Population density maps (MLX plots) which represent the covalent compounds of an element as a function of all the known ligands are exemplified for chromium; molybdenum and tungsten; and nickel, palladium and platinum. These plots are used to identify the major characteristic chemical properties of the elements including reactivity trends and reaction mechanisms.