Question

Helium atom has 2 electrons in its valence shell but its valency is not 2.
(A)- True
(B)- False

Answer 1

Hint: Helium is called noble gas or inert gas. Noble or inert elements are the most stable due to having the maximum number of valence electrons their outer shell or valence shell can hold. Helium has no tendency to form any chemical bonds due to highly stable configuration.

Complete step by step answer:
> Valency of an element is defined as its tendency to accept valence electrons from other atoms or to give its own valence electrons, in other words we can say, valency is the ability of an atom of a given element to attach to a certain number of other atoms.
> Valency is defined as the tendency of an element to combine with a hydrogen atom. The number of hydrogen atoms bonded to that element gives its valency.
> The atoms try to reach a stable state by gaining some electrons or losing some electrons.
> A helium atom has only one shell (K shell) which can have a maximum of 2 electrons. Thus, its shell is already complete, called a duplet. It can neither lose electrons nor gain electrons.
> Helium doesn’t lose or gain any electron from its valence shell hence the valency of helium is zero.

According to the above-mentioned points, we can conclude that the above-mentioned statement is true. More specifically we can write, a Helium atom has 2 electrons in its valence shell but its valency is zero.

Note:
An element can show variable valency. This happens because of the availability of vacant orbitals in the outermost valence shell. This variable valency is sometimes referred to as the oxidation state of the element.