Hello, I need to understand the following: Considering an element Sulfur - S which has 16 electrons. How do we calculate the valency electron of S? Please correct me if I am wrong:2+2+6+2+4=16. So, the valency electron = 4+2=6 Is it that always valency electron is the addition of the last two shells? In that case for Na, sodium, if we take 11 and arrange it as 2+2+6+1, then the valency electron is 1 or 6+1? Now, considering the fact valency electron is 1, if we go by, up down up down rule, then as it is 1, hence the spin is up? For 6: is it up(1) down(2) up(3) down(4) up(5) down(6) as it is both up/down hence it would be +-1/2 spin? For Phosphorous 2,8,5, what would be the valency electron 5 or 13? If 5 then up down up down up, will it have a up spin? Is it that for even numbers like 4,6 the spin will be both up/down i.e. +-1/2? Kindly let me know.