MCAT Chemistry Question — Gold Electrons

  • Reviewed By: Liz Flagge
  • How many electrons does gold (Au) possess that have a quantum number l = 2?

    A) 10

    B) 23

    C) 30

    D) 79


    You must know that the quantum number l can take on four different values: 0, 1, 2, and 3. Furthermore, you must know that each number corresponds to a particular orbital: 0=s, 1=p, 2=d, 3=f. So the question is asking us how many d electrons gold possesses.

    Since gold is in the sixth period, it has the following d orbitals: 3d, 4d, and 5d. The 3d and 4d orbitals are filled with 10 electrons each, and the 5d orbital has 10 electrons, giving a total of 30. Therefore the correct answer is C, 30.

    (If you’re wondering why gold has 10 electrons in its 5d orbital instead of 9, the answer is related to the high stability of a fully-filled d subshell. From the periodic table alone, you would think that gold had 9 5d electrons, but it becomes significantly more stable if one 6s electron moves up to fill the 5d subshell. This explains why the 5d subshell holds 10 electrons!)

    Want more MCAT practice?

    We’ve got options for every schedule and learning style!

    From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

    Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

    Schedule My Free Consultation

    Create your Free Account to access our MCAT Flashcards SIGN UP NOW

    MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.

    Leave a Reply

    Your email address will not be published. Required fields are marked *