The elements of group 12, (formerly called group IIb in North America and IIa in Europe) are known as the zinc group and include the metals zinc, cadmium, mercury (and, nominally, ununbium, element 112). The atoms of the elements in group 12 have 2 valence electrons. The elements occur at the end of the three transition series of metals. Unlike their immediate predecessors in the coinage group, zinc group metals combine or react with other elements only by using their outer s-electrons. Other characteristics that differentiate the zinc group from the metals of the transition series are the group members' realtively low melting points and boiling points, and their tendency to form colorless and diamagnetic ions, in contrast to the other transition metals' colored ions and many instances of paramagnetism. Further, the zinc group does not display the variable valency characteristic of other transition metal ions. On the other hand, the zinc group shares with the other d-block elements the ability to form many coordination compounds.