Question

Why does pottasium and calcium have configuration of 2,8,8,1 and 2,8,8,2 instead of 2,8,9 and 2,8,10

Answer 1

Potassium had electronic configuration 2,8,8,1 instead of 2,8,9  because the outer most shell tends to have 8 electrons and that one electron can be donated or pair up  with another electron but the latter configuration does not allow such a phenomena to take place..

Calcium has the electronic configuration 2,8,8,2 instead of 2,8,10 the same reason as state above & also because the octate configuration is a more stable configuration than filling up the 10 electrons.

Answer 2

potassium has 2,8,8,1 configuration is bcas the 3rd shell should have 8 electrons according to the rule of octaves.
same for calcium