Question

The `Z_(eff)` for
3d electron of `Cr`
`4s` electron of `Cr`
`3d` electron of `Cr^(3+)`
`3s` electron of `Cr^(3+)` are in the order respectively
A. 4.6,2.95,4.95,8.05
B. 4.95,2.95,4.6,8.05
C. 4.6,2.95,5.3,16.55
D. none of these

Answer 1

Correct Answer - C
`[C_(r) = 1s^(2) 2s^(2) 2p^(6) 3s^(2)3p^(6) 4s^(1) 3d^(5)`
`Z_(eff) =` Atomic no `sigma`
s for 4s electron (valence shell `e^(-) -1) xx 0.35 +`
Penultimate shell `e^(-) xx 0.85 + `remaining `e^(-)`
`= (1-1) xx 0.35 +13 xx 0.85 +10`
`= 0 + 11.05 +10 = 21.05`
`Z_(eff) = 24 - 21.05 = 2.95`
`Z_(eff)` for 3d electron
`sigma` for `3de^(-) =` (valence shell `e^(-)-1) xx 0.35 +` remaining `e^(-)`
`= (5-1) xx 0.35 +18`
`= 1.4 +18 = 19.4`
`24 - 19.4 = 4.6]`