MCAT General Chemistry Question 250: Answer and Explanation

Home > MCAT Test > MCAT general chemistry practice tests

Test Information

Question: 250

4. The first, second, and third ionization energies for strontium are 549.5 kJ/mol, 1064.2 kJ/mol, and 4138 kJ/mol respectively. Why is the third ionization energy so much higher than the first two ionization energies?

  • A. The third electron is being removed from a completely full subshell.
  • B. The third electron has a larger mass than the first two electrons being removed.
  • C. The third electron being removed is less attracted to the nucleus than the first two electrons.
  • D. The third electron is at a higher energy level than the first two electrons.

Correct Answer: A

Explanation:

A All electrons in an atom have the same mass, eliminating choice B. To remove three electrons from Sr, the first two electrons are removed from the 5s subshell and the third electron is removed from the 4p subshell, eliminating choice D. Since the third electron is at a lower energy level, it experiences less shielding and would be more attracted to the nucleus than the first two electrons removed, eliminating choice C. The third electron comes from the completely full 4p subshell and is much more difficult to remove, making choice A the best answer.

Previous       Next