Write down the electronic configuration of Co 2 +

Co 2 + is formed by the loss of two electrons from the 4 s orbital of the cobalt atom. It has now a total of 25 electrons. Therefore, the electronic configuration can be given as 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 7 or Ar 3 d 7 .

Name the members of the lanthanoid series which exhibit + 4 oxidation state and those which exhibit + 2 oxidation states. Try to correlate this type of behaviour with the electronic configuration of these elements.

The lanthanoids that exhibit + 4 oxidation state are cerium, terbium, promethium and neodymium. Cerium and terbium shows + 4 oxidation. This can be explained in the terms of extra stability of half filled and completely filled 4 f sub-shell respectively in their + 4 oxidation state. Promethium and neodymium shows + 4 oxidation stable because both these tetra positive ions are excess of one or two electrons respectively from the necessary 4 f -sub-shell stable configuration. The lanthanoids that exhibit + 2 oxidation states are europium, ytterbium, samarium and thulium. The + 2 oxidation state of europium and ytterbium can be explained in terms of the extra stability of half filled and completely filled 4 f -sub-shell. Similarly, the + 2 oxidation states of samarium and thulium is because these ions are short of one electron from the necessary half filled and completely filled stable configurations.