Question

The property of the transition elements is that they have incomplete penultimate shell. Then why potassium and calcium are not placed in the transition metals because they have configuration of 2,8,8,1and 2,8,8,2 respectively. Their penultimate shell is also incomplete.

Answer 1

Dear Student,
The transition elements are the d-block elements in which the differentiating electron enters the (n-1)d sub-shell. The electronic configuration of potassium of potassium and calcium which is 2,8,8,1 and 2,8,8,2 respectively shows that the differentiating electron is entering in 4s sub-shell and not in 3d sub-shell as according to Afbau's principle 4s sub-shell is more stable than 3d sub-shell. Therefore as differentiating electron is entering into s sub-shell in potassium and calcium they are s-block elements. Moreover the differentiating electron is not entering in (n-1)d orbital and therefore these elements are not transition elements.
Regards