MCAT General Chemistry Question 29: Answer and Explanation

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Question: 29

14. Why do halogens often form ionic bonds with alkaline earth metals?

  • A. The alkaline earth metals have much higher electron affinities than the halogens.
  • B. By sharing electrons equally, the alkaline earth metals and halogens both form full octets.
  • C. Within the same row, the halogens have smaller atomic radii than the alkaline earth metals.
  • D. The halogens have much higher electron affinities than the alkaline earth metals.

Correct Answer: D

Explanation:

Ionic bonds are formed through unequal sharing of electrons. These bonds typically occur because the electron affinities of the two bonded atoms differ greatly. For example, the halogens have high electron affinities because adding a single electron to their valence shells would create full valence shells. In contrast, the alkaline earth metals have very low electron affinities and are more likely to be electron donors because the loss of two electrons would leave them with full valence shells. Choice (A) states the opposite and is incorrect because the halogens have high electron affinity and the alkaline earth metals have low affinity. Choice (B) is incorrect because equal sharing of electrons is a classic description of covalent bonding, not ionic. Choice (C) is a true statement, but is not relevant to why ionic bonds form.

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