B. E. Douglas, D. H. McDaniel, J. J. Alexander, Concepts and Models of Inorganic Chemistry, 3rd edition, John Wiley & Sons, New York, 1994, page 52.

Problem 1.14

Write the electron configuration beyond the noble gas core and give the number of unpaired electrons (for example, F-, [He]2s22p6) for K+, Ti3+, Cr3+, Fe2+, Cu2+, Sb3+, Se2-, Sn4+, Ce4+, Eu2+, and Lu3+.
 
 

Answer:
 
Ion
Electron Configuration
Number of Unpaired Spins
K+
[Ar]
0
Ti3+
[Ar]3d1
1
Cr3+
[Ar]3d3
3
Fe2+
[Ar]3d6
4
Cu2+
[Ar]3d9
1
Sb3+
[Kr]4d105s2
0
Se2-
[Kr]
0
Sn4+
[Kr]4d10
0
Ce4+
[Xe]
0
Eu2+
[Xe]4f7
7
Lu3+
[Xe]4f14
0