how can we determine the valency of an element by only looking at the distribution of electrons in K L M N orbits ?

The valency can be easily calculated with the help of distribution of electrons by using rules

 

Rule 1 :  if the valence electrons are less than 4 than the valency = no of valence electrons

 

 

Rule 2: If the valence electrons are greater than 4 the valency= 8 -  no of valence electrons