What is the ground-state electron configuration of an iron atom (atomic number 26)?
Answer and explanation
Correct answer: B. [Ar] 4s2 3d6
- Step 1: Argon accounts for 18 electrons. Step 2. The remaining 8 go into 4s (2) and 3d (6). Answer: [Ar] 4s2 3d6. Why not the others: [Ar] 4s2 3d8 represents nickel with 28 electrons; [Ar] 3d8 omits the lower-energy 4s valence orbital; and [Ar] 4s1 3d7 represents an excited non-ground state configuration.
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