Question

Define Z-effective for: He, Mercury, Xenon, Argon and Neon ? Please explain

Answer 1

The effective nuclear charge Zeff is the net positive charge experienced by an electron in a multi-electron atom.

The formula for effective nuclear charge is

Zeff=Z–S

where

Z is the number of protons in the nucleus, and
S is the shielding constant, the average number of electrons between the nucleus and the electron in question..

The shielding constant for each group is formed as the sum of the following contributions:

• All other electrons in the same group as the electron of interest shield to an extent of 0.35 nuclear charge units except 1s group, where the other electron contributes only 0.30.
• If the group is of the [s, p] type, an amount of 0.85 from each electron (n-1) shell and an amount of 1.00 for each electron from (n-2) and lower shell.
• If the group is of the [d] or [f] type then an amount of 1.00 for each electron from all lying left to that orbital.

Zeff=Z–S=2–0.30=1.70

Z_eff(Ne) = 10 - 2 = 8

Z_eff(Ar) = 18 - 11.25 = 6.75

Z_eff(Ne) = 10 - 4.15 = 8.