( a ) There are two types of valencies in metals: primary and secondary valencies. Primary valencies are satisfied by negative ions, and secondary valencies are filled by both neutral and negative ions.

( b ) Around the central atom, a metal ion has a fixed number of secondary valencies. These valencies also orient themselves in a specific direction in the space afforded by the coordination compound’s specified geometry.

(c) Secondary valencies cannot be ionized, although primary valencies can be ionosed.