Multiple Choice
Which of the following represents the noble gas electron configuration of bismuth (Bi)?
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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 manganese (Mn)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^6
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5
Verified step by step guidance1
Identify the atomic number of manganese (Mn), which is 25. This means Mn has 25 electrons to be placed in orbitals according to the Aufbau principle.
Recall the order of orbital filling based on increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Fill the orbitals in order until all 25 electrons are assigned: 1s^2 (2 electrons), 2s^2 (2 electrons), 2p^6 (6 electrons), 3s^2 (2 electrons), 3p^6 (6 electrons), 4s^2 (2 electrons), and then place the remaining electrons in 3d orbitals.
Apply Hund's rule and the stability associated with half-filled d subshells: a half-filled 3d subshell (3d^5) is more stable than a 3d^6 configuration, so electrons will arrange to maximize unpaired electrons in 3d.
Conclude that the correct ground-state electron configuration for Mn is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5$, reflecting the stable half-filled d subshell.
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