Question

which one of the following atoms has 5 unpaired electrons in its ground electronic state?
a. cr (z = 24)
b. ba (z = 56)
c. ga (z = 31)
d. k (z = 19)
e. te (z = 52)

Explanation:

Step1: Write electron configurations

• For \(Cr(Z = 24)\): The electron configuration is \([Ar]3d^{5}4s^{1}\). In the \(3d\) sub - shell, there are 5 unpaired electrons (since each \(d\) orbital can hold 2 electrons and in \(d^{5}\), all 5 \(d\) orbitals have one unpaired electron each) and 1 unpaired electron in \(4s\).
• For \(Ba(Z = 56)\): The electron configuration is \([Xe]6s^{2}\). Both electrons in \(6s\) are paired.
• For \(Ga(Z = 31)\): The electron configuration is \([Ar]3d^{10}4s^{2}4p^{1}\). There is 1 unpaired electron in \(4p\).
• For \(K(Z = 19)\): The electron configuration is \([Ar]4s^{1}\). There is 1 unpaired electron in \(4s\).
• For \(Te(Z = 52)\): The electron configuration is \([Kr]4d^{10}5s^{2}5p^{4}\). In the \(5p\) sub - shell (\(p\) has 3 orbitals), there are 2 unpaired electrons (using Hund's rule, electrons first fill orbitals singly).

Answer:

A. \(Cr(Z = 24)\)