Question

Screening constant for $3d$ electron in zinc grouping of orbitals is:

Answer 1

Screening constant is the summation of contribution of each electron according to the slater’s rule. The contribution of each orbital electrons is different to the screen constant. The value of each orbital contribution is given by Slater's rule.

Complete step by step answer:
Let us understand what is meant by the screening constant.
Screening constant can be referred to as the measure of screening of electrons from the force of the nucleus. Screening effect is the effect of electron with respect to its position in the atom
Slater’s rule tells us the contribution made by different orbitals for screening effect.
$n \to 0.35$
$n - 1 \to 1.0$
Where $n$ is the orbital for which the screening effect has to be calculated.
Let us write down the electronic configuration for zinc.
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^{10}}$
Now, in the question the orbital in mention is $3d$
So,
$\sigma = 0.35 \times n + 1.0 \times (n - 1)$
Where, $\sigma$ = Screening constant
Here,
$n = 9$ electrons
$n - 1 = 18$ electrons
So, we get:
$\sigma = 0.35 \times 9 + 1.0 \times (18)$
So we get
$\sigma = 21.15$

Note: There is another type of effect known as the shielding effect which is often confused with the screening effect.
Every electron in the atom is constantly attracted to the nucleus which is a rich positively charged centre. However, the electrons in the atom cause repulsive forces. This leads to a net decrease in the force of attraction that an electron feels by the nucleus.
So, the decrease in effective nuclear charge by an electron due to the inner electrons, since they reduce its effect is known as shielding effect.
However, Screening effect is of the electron itself. It is the decrease in nuclear pull which is felt by the electron as the size keeps increasing. Electrons in the f orbital feel less nuclear force due to its diffused shape as compared to the electrons in the s orbital. It can be said that it is the ease with which an electron can be removed.