Question

Helium atom has 2 electrons in its valence shell. But, it's valency is not 2. Justify.

Explain with complete justifications.

Points : 15 ☺

Answer 1

valency is the number of electrons lost or gained from the outermost shell of an atom to attain stable electronic configuration.

we know ,
an atom attains stable electronic configuration by two ways:-
1) by duplet structure - having 2 electrons in there outermost shell
2)by octet structure- having 8 electrons in their outermost shell.

The atom helium has 2 electrons in its outermost shell.
therefore it has stable electronic configuration with duplet structure.

since it is stable it does not gain, lose or share electrons and is chemically non reactive and inert.

So, it's valency is 0 not 2

Answer 2

Helium has only one energy shell that is K-shell

Number of electrons that can be accommodated in a given energy shell is given by 2n²

K-shell is the 1st energy shell

So, number of electrons that can be accommodated = 2(1)² = 2

Even the electronic configuration is 2

Helium is stable and inert.

Hope This Helps You!