Question

Helium atom has 2 electrons in its valence shell but its valency is not 2. Explain.

Answer 1

Helium has only 1s orbital and it is completely filled by 2 electrons.

1s orbital can accomodate 2 electrons and those are filled and it achieved octect.

It's valency is '0' because it has completely filled orbital(s).

:)

Answer 2

Helium completes a duplet with its electronic configuration being 2. It generally do not take part in chemical reactions and is considered a zero valent element.

in its outermost shell is completely filled.and is inert in the K shell the total elecrons that can be accomodated is 2 .for helium the elctronic confrigution is = 2.hence it doesn't require to gain or loose any electron to become inert.