Multiple Choice
Which of the following best represents the ground state electron configuration of a halogen?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct electron configuration for a neutral iron (Fe) atom?
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 3d^6 4s^2
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8
D
1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 4s^2
Verified step by step guidance1
Identify the atomic number of iron (Fe), which is 26. This means a neutral iron atom has 26 electrons to arrange in its electron configuration.
Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Fill the orbitals in order, adding electrons until you reach 26 total: 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 finally 3d^6 (6 electrons).
Note that although 3d orbitals come after 4s in energy when filling, the 4s orbital is filled before 3d because it is lower in energy for neutral atoms.
Compare the given options to the correct order and electron count, confirming that the configuration 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6 correctly represents the neutral iron atom.
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