What is screening effect ?

Explanation

The repulsive force between inner shell electrons and the valence electrons leads to a decreases in the electrostatic attractive forces acting on the valence electrons acts as a shield between the nucleus and the valence electrons
Pauling 's scale :
(i) Electronegativity is the relative tendency of an element present in a covalently bonded molecule to attract the shared pair of electrons towards itself.
(ii) Pauling assigned arbitrary value of electro negativities for hydrogen and fluorine as 2.2 and 4 respectively .
(iii) Based on this the electro negativity values for other elements can be calculated using the following expression .
`(X_(A)-X_(B))=0.182sqrt(E_(AB)-(E_(A A)xxE_(BB))^(1//2))`
Where `E_(AB),E_(aa)andE_(b b)` are the bond dissociation energies of `AB,A_(2)andB_(2)` molecule respectively `X_(A)andX_(B)` are elctro negativity values of A and B.