Question

how do we calculate valency?

Answer 1

Here is your answer
The number of electrons needed to Complete the octet of an element is subtracted by the no. Of electrons present in the outermost shell is called valency

Answer 2

It depends on the north of atom required by an element to be stable like nearest noble gas.
metals have valncy 1,2,3. so they loses electrons to be stable and number of electrons it loses it becomes it's valency electrons .It is marked as positive mark +2,+1,+3.


non metals have valency electrons 4,5,6,7.
so it gains electrons to be stable so the numbed of electrons it gains becomes it's valency electrons. It is maked with negative mark. like -4,-5,-6,-7


Ex..
like a metal has atomic number 11. so its. electronic configuration is 2,8,1. so to be stable like argon it need to remove one electron so it loses one electron and becomes stable like argon. 2,8 and it's valency become +1