Question

how to find valencies of elements with their atomic number

Answer 1

hi...
here is your answer:

Lets take example:

i) sodium: atomic number = 11
Electronic configuration : 2,8,1
valency = +1

ii) oxygen: atomic number = 8
Electronic configuration : 2,6
valency = (8-6) = 2

iii) Carbon: atomic no. =6
Electronic configuration : 2,5
valency = ±4

hope u will understand from these examples :-)