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## What is screening effect or shielding effect ?

There are two Methods to calculate Screening constant or shielding constant

**1. Experimental method :** in this method if ionisation energy is given, we can apply I.E. = 13.6Zeff^2/n^2 from which Zeff can be calculated. So Zeff = Z – b, b can be calculated.

**2. Theoritical method:** this is an approximate method in which different orbital electrons are assigned different in screening constant.

If we have to find b for nth shell electrons

(n+1, n+2, n+3) has 0 contribution in b

nth shell e has 0.35 times their number-1 because for 1 electron, we have to find b, so all other e will contribute in b

(n-1) shell e contribution in b depends on orbital type. If e is in (n-1)d or f then its contribution is 1 times their number and if e is in (n-1)s or p then its contribution is 0.85 times their number.

(n-2, n -3) shell e contribute 1 times their number in b.

e.g. for

Zn: 1S2 2S2 2P6 3S2 3P6 4S2 3d10

b for 4s e = 0.35×1+0.85×8+1×10+1×8+1×2

For 3P e = 0×2+0.35×17+0.85×8+1×2

Sir, it is an approximate method, so there are some slight changes in contribution in b but most of the book follow this contribution rule..