Question

How to find the valency of an element using spdf trick?

Answer 1

To find the valency of an element by using spdf trick;

for ex : we take magnesium .

The atomic number of Magnesium is 12,

Now let us write the electronic configuration of Magnesium;

1s*2 2s*2 2p*6 3s*2


In the last shell ; i.e

3s*2 is the last shell . we have 2 electrons.
so , 2 is the valency

For example we take an another element, Scandium ( atomic no. is 21 )

1s*2 2s*2 2p*6 3s*2 3p*6 4s*2 3d*1

now , 4s*2 is the last shell , So 2 is the valency

Next we take chlorine,

1s*2 2s*2 2p*6 3s*2 3p*5

here 3s*2 3p*5 is the last shell
but here 7 is not the valency

now we have to subtract 7 from 8.
so the valency is 1.

NOTE:
1 electron - valency is 1
2 electrons - valency is 2
3 electrons - valency is 3
4 electrons - valency is 4
5 electrons - valency is 3 ( 8-5 )
6 electrons - valency is 2 ( 8-6)
7 electrons - valency is 1 ( 8-7)
8 electrons - valency is 0 (8-8)
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Answer 2

find the valency of an element then first write the electronic configuration of an element after that the loss electronic is the valency of element