Question

The $Z_{eff}$ for
3d electron of Cr
4s electron of Cr
3d electron of ${Cr}^{3+}$
3s electron of ${Cr}^{3+}$ are __________ respectively.

• A. 4.6, 2.95, 4.95, 8.05
• B. 4.95, 2.05, 4.6, 8.05
• C. 4.6, 2.95, 5.3, 12.75
• D. none of these

Answer 1

Answer: (C)

4.6, 2.95, 5.3, 12.75

Cr ${1s}^2{2s}^2{2p}^6{3s}^2{3p}^6{3d}^5{4s}^1$

${24}^{-}$

Using later's rule:

for $3d{e}^{-}{Z}_{eff}=24-(4\times 0.35)-(18\times 1)=4.6$

for $4s{e}^{-}{Z}_{eff}=24-(0\times 0.35)-(13\times 0.85)-(10\times 1)=2.95$

$C{r}^{3+}\left({1s}^2{2s}^2{2p}^6{3s}^2{3p}^6{3d}^3\right)$

for $3d{e}^{-}{Z}_{eff}=24-(2\times 0.85)-18=5.3$

for $3s{e}^{-}{Z}_{eff}=24-(7\times 0.35)-(8\times 0.85)-(2\times 1)=12.75$

$s^1{p}^6$ $2\left(s^2{p}^6\right)$ ${1s}^2$