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Friday, July 23, 2021

Slater's Rules: (Estimating the extent of shielding):

The quantitative prediction of specific energy level is not possible if an atom have more than one electron (multi-electrons system). In multi-electron system each electron acts as a shield for electron further away from the nucleus, reducing the attraction between the nucleus and distant electron. The Slater provides a set of rules which help to predict the extent of shielding.

In the Slater rule determine the actual charge felt by an electron and also allow you to estimate the effective nuclear charge Zeff  from the real number of protons in the nucleus and the effective shielding of electrons in each orbital "shell"

“Slater defined Z* or Zeff (effective nuclear charge) as a measure of nuclear attraction for an electron. Or The magnitude of  positive charge “experienced” by an electron in the atom.

                                              Thus Z* =Z-S

Where Z is the (nuclear charge)= The number of protons in the nucleus of an atom,  and S represent the shielding constant and value is greater than zero but less than Z.

Step 1: Write the electron configuration of the atom in the following form:

              (1s) (2s, 2p) (3s, 3p) (3d) (4s, 4p) (4d) (4f) (5s, 5p) . . .


Step (2):  Electron in higher group do not shield the electrons in the lower group.

Step (3): For ns and np valence electrons:

(A) The electrons in same ns and np group contribute 0.35, except the 1s which shield 0.30

(B) Electrons within the n-1 group contribute 0.85

(C) Electrons within the n-2 or lower groups contribute (shield) 1.00

Step (4): For nd and nf valence electrons:

(A) Electrons in same nd and nf group contribute 0.35

(B) Electrons in the group to the left contribute 1.00

Shielding constant (S) obtained is subtracted from Z to get Z*

 Solved Questions:

(1) What is the shielding constant (S) experienced by a 3d electron in the bromine atom?

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