How many electrons does a cobalt (Co) atom have in its 3d subshell?

• A. 5
• B. 6
• C. 7
• D. 10

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of cobalt (Co), which tells you the total number of electrons in a neutral atom. Cobalt has an atomic number of 27, so it has 27 electrons.
2. Recall the electron configuration order for transition metals, focusing on the filling of the 3d subshell after the 4s subshell. The general order is: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
3. Write the electron configuration for cobalt: start by filling the lower energy orbitals up to 4s. This gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² before filling the 3d subshell.
4. Determine how many electrons go into the 3d subshell by subtracting the electrons accounted for in all orbitals before 3d from the total 27 electrons. The 3d subshell will have the remaining electrons.
5. Conclude the number of electrons in the 3d subshell for cobalt based on the electron configuration, which is the number of electrons after filling 4s² and before moving to 4p orbitals.