The essential valency is the number of negative particles that have the same charge as the metal particle.
It represents the metal's oxidation number.
Ionizability exists for the primary valencies.
Primary valency is Non-Directional are:
Metals have two kinds of valencies: primary/ionizable valency and secondary / non-ionizable valency.
Every metal atom is capable of satisfying both its primary and secondary valencies.
Secondary valency ligands are always directed towards fixed positions in space, giving the complex a definite geometry, whereas primary valencies are non - directional.