CBSE Class 11-science Answered

The electron configuration for chromium is 1s²2s²2p⁶3s²3p⁶4s²3d⁴.

However, in the case of chromium there is one empty d sub orbital, one of the electrons from the 4s orbital will move up to the 3d orbital and make the the actual electron configuration 1s²2s²2p⁶3s²3p⁶4s¹3d⁵. 

Therefore,

Predicted electron configurations: Cr (Z = 24): [Ar] 4s² 3d⁴

Actual electron configurations: Cr (Z = 24): [Ar] 4s¹ 3d⁵

Quantum number for chromium

(From the above table, we get,)

Predict its number of subshells

Ans: Chromium has 10 subshells viz - 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f

Number of electrons in subshell having l=0

Ans: There are 4 subshells and the first three sub shells (n=1, n=2 and n=3) has 2 electrons each and (n=4) has 1 electron.

Number of electrons having n + ℓ value=3

Ans: Total 8 electrons has n + ℓ value=3.

Number of electrons in highest value of n

Ans: Highest value is the last orbital (N orbital); n=4 i.e, 1 electron.