Question
Thu January 05, 2012 By:
 

WHAT IS SHIELDING / SCREENING EFFECT, INERT PAIR EFFECT ? HOW DOES THE INTERVENTION d AND f BLOCK CHANGE THE PROPERTIES OF GROUP 13 ELEMENTS?

Expert Reply
Fri January 06, 2012

In 1930 J. C. Slater devised a simple set of guidelines for shielding or screening constants ( s). For a 1s electron, s = 0.3

 

For electrons in an s or p orbital with n > 1, the screening constant is given by  

                         s = 1.00 N2 + 0.85 N1 + 0.35 N0 

 N0 represents the number of other electrons in the same shell, N1 represents the number of electrons in the next smaller shell ( n - 1 )th shell, and N2 is the number of electrons in other smaller shells ( n - 2 and smaller shells ).

Lets calculate screening constant for an electron in the fluorine 2s orbital,

Electronic configuration of fluorine = 1s2 2s2 2p5

 N0 = 6 ( the electron of interest in the L shell is not counted), N1 = 2 (these are the 1s electrons), and N2 = 0 (there are no other inner shells). The Slater rules predict

S = 0.85 ( 2 ) + 0.35 ( 6 ) = 3.8

n stands for principle quantum number. For 1s, n=1; 2s, n=2; 2p, n=2; 3d n=3.

For example, if we are calculating Screening constant for any electron of n shell, (n-1)th shell means other shells which are before that principal quantum number; example we are calculating for 2s orbitals electron, then (n-1)th shell is 1s;

Inert pair effect: 

The inert pair effect is the tendency of the outermost s electrons to remain nonionized or unshared in compounds of post-transition metals. 

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