MCAT General Chemistry Question 183: Answer and Explanation

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Question: 183

3. A pure sample of which of the following ions/molecules will participate in intermolecular hydrogen bonding?

I. CH₃CO₂H

II. CO₂

III. H₂S

A. Li
B. Be
C. C
D. N

Correct Answer: D

Explanation:

D Since Li has only one valence electron and Be has only two, neither choices A nor B can be correct. To choose between C and D, note that the valence configuration of C is 2s²2p². Thus the 2s electrons are paired leaving only two unpaired p electrons. Nitrogen has a valence configuration of 2s²2p³, and by Hund's rule, the three p electrons will singly occupy the p_x, p_y, and p_z levels rather than pairing up to avoid electron repulsion.

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