MCAT Chemistry Question — Chromium
- Jul 23, 2017
- MCAT Question of the Day
A. [Ne] 4s23d4
B. [Ar] 4s23d4
C. [Ar] 4s13d5
D. [Ne] 3d6
Click for Explanation
A. [Ne] 4s23d4, incorrect, The correct orbital shorthand is [Ar].
B. [Ar] 4s23d4, incorrect, While this would normally be true, Cr and Cu are exceptions which fill their 3d orbitals to 5 and 10 before placing their last electron in 4s1.
C. [Ar] 4s13d5, correct.
D. [Ne] 3d6, incorrect, [Ar] is the correct shorthand rather than [Ne], and the correct orbital filling is shown in answer c). Note that chromium is an exception to the orbital filling guidelines.
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