Multiple Choice
Which of the following is the correct full ground-state electron configuration for the element phosphorus (atomic number 15)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct ground-state electron configuration for the Co^{3+} ion?
A
[Ar] 3d^7
B
[Ar] 4s^2 3d^5
C
[Ar] 3d^6
D
[Ar] 4s^1 3d^6
Verified step by step guidance1
Step 1: Identify the atomic number of cobalt (Co), which is 27, meaning a neutral Co atom has 27 electrons.
Step 2: Write the ground-state electron configuration for neutral Co: $[\mathrm{Ar}]\,4s^2\,3d^7$.
Step 3: Understand that when forming the $\mathrm{Co}^{3+}$ ion, three electrons are removed from the neutral atom. Electrons are removed first from the outermost shell, which is the 4s orbital, followed by the 3d orbitals.
Step 4: Remove two electrons from the 4s orbital and one electron from the 3d orbital to account for the $3+$ charge, resulting in the configuration $[\mathrm{Ar}]\,3d^6$.
Step 5: Confirm that the correct ground-state electron configuration for $\mathrm{Co}^{3+}$ is $[\mathrm{Ar}]\,3d^6$, as electrons are lost from 4s before 3d orbitals.
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