Valency :- “It is the combining capacity of an atom”.
it also indicates the number of electrons that can be gained , lost or shared . It decides that how many bonds can be formed, it gives the idea of molecule formation and the type of bond formed.
calculation of valency is a simple task lets do it,
Step 1 : calculate the number of electrons present in the outermost shell.
Step 2 : now here two conditions arise :-
- If the number of electrons is smaller than four ( <4) then the valency is equal to the number of electrons.
valency = number of electrons
2. If the number of electrons is more than four (>4) then the number of electrons are subtracted from eight.
valency = 8 – number of valence electrons.
foe example we have to calculate the valency of
(a) sodium(atomic number = 11) : here is the configuration :-
K shell = 2 electrons
L shell = 8 electrons
M shell= 1 electron
number of valence electrons ( the electrons present in outermost shell) = 1
and Valency = 1
(b) oxygen(atomic number = 8) : here is the configuration:-
K shell = 2
L shell = 6
number of valence electrons = 6
now the valency = 8 – 6 = 2
valency = 2
(c) Carbon(atomic number 6): here is the configuration
K shell = 2
L shell = 4
now here the outermost or valence electrons are 4 so we can find valency by any method and that will be four only
so valency of carbon = 4