Question

question 8 (1 point) how many unpaired electrons does co³⁺ have? a) 6 b) 1 c) 4 d) 0 e) 3

Explanation:

Step1: Write electron - configuration of Co

The atomic number of Co (cobalt) is 27. The electron - configuration of Co is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{7}$.

Step2: Determine electron - configuration of $Co^{3 + }$

When Co loses 3 electrons to form $Co^{3+}$, the 4s electrons are lost first, followed by one 3d electron. So the electron - configuration of $Co^{3+}$ is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{6}$.

Step3: Analyze the 3d sub - shell

In the 3d sub - shell, there are 5 orbitals. According to Hund's rule, electrons first fill each orbital singly before pairing up. For $3d^{6}$, after filling 5 orbitals singly, the 6th electron will pair up with one of the electrons in the 5 orbitals. So the number of unpaired electrons is 4.

Answer:

C. 4