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 :-

1. 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

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