Question

$Z_{eff}$ for 4s electron in Zn (atomic no. = 30) is:

• A. 1.65
• B. 14
• C. 12.85
• D. 4.35

Answer 1

The correct option is D 4.35

$Zn\left(30\right)=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^2$
$Z_{eff}=Z-\sigma$
4s is filled and we want to calculate $Z_{eff}$ for electon in 4s. Let 4s shell to be the n shell
So we have electrons corresponding to each shell are as:
$n\to 1;(n-1)\to 18;(n-2)andbelow\to 10$
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> $\sigma =0.35\times 1+0.85\times 18+1\times 8+1\times 2=25.65$
$\Rightarrow Z_{eff}=30-25.65=4.35$