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.
