Question

Helium atom has 2 electrones in its valence shell but its valency is not 2, explain

Answer 1

it is because helium has two atom which are placed in the first cell and the first cell can only hold two electrons which is full .

Answer 2

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

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