Question

Choose the incorrect statement about effective nuclear charge.

• A. $Z_{eff}=Z-\sigma$ $(\sigma$ is Slater's screening constant)
• B. $Z_{eff}$ increases as we move across the period
• C. $Z_{eff}$ decreases from top to bottom in a group
• D. $Z_{eff}$ is constant or almost constant for f-block elements

Answer 1

The correct option is D $Z_{eff}$ is constant or almost constant for f-block elements

A. The effective nuclear charge is the difference between the nuclear charge and the shielding by valence electrons. It is given by the expression, $Z_{eff}=Z-\sigma$. Here, $\sigma$ is Slater's screening constant. Hence, option A is correct.

B. On moving from left to right across a period, the value of the effective nuclear charge increases. Hence, option B is correct.

C. On moving from top to bottom in a group, the value of the effective nuclear charge decreases as the shielding effect of inner electrons increases. Hence, option C is correct.

D. There is a gradual increase in the effective nuclear charge for the f-block elements. Hence, option D is incorrect.