MCAT General Chemistry Question 17: Answer and Explanation

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Question: 17

2. Carbon and silicon are the basis of biological life and synthetic computing, respectively. While these elements share many chemical properties, which of the following best describes a difference between the two elements?

  • A. Carbon has a smaller atomic radius than silicon.
  • B. Silicon has a smaller atomic radius than carbon.
  • C. Carbon has fewer valence electrons than silicon.
  • D. Silicon has fewer valence electrons than carbon.

Correct Answer: A

Explanation:

As one moves from top to bottom in a group (column), extra electron shells accumulate, despite the fact that the valence configurations remain identical. These extra electron shells provide shielding between the positive nucleus and the outermost electrons, decreasing the electrostatic attraction and increasing the atomic radius. Because carbon and silicon are in the same group, and silicon is farther down in the group, silicon will have a larger atomic radius because of its extra electron shell.

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