MCAT General Chemistry Question 182: Answer and Explanation
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Question: 182
2. Which of the following atoms/ions has electrons in the subshell of highest energy?
- A. [Ar] 4s23d6
- B. [Ar] 4s23d4
- C. [Ar] 3d6
- D. [Ar] 4s23d2
Correct Answer: C
Explanation:
C When answering electron configuration questions, the first step is to eliminate all answer choices that do not display the correct number of electrons. In this case, ferrous ion possesses six electrons beyond those represented by [Ar] (eight for elemental iron minus two to generate the +2 cation). Thus, choices A and D can be eliminated. To choose between B and C, recall that when transition metals ionize, it is the outermost and therefore least tightly held electrons that are removed first. In this case, the 4s electrons are further from the nucleus and are less tightly held (n = 4 represents a greater radial distance from the nucleus than n = 3). Thus they are the first to be removed.