MDCAT Chemistry MCQ #937

Why does the 4s orbital fill before the 3d in potassium's electron configuration?

MDCAT Chemistry MCQ #937

  1. Question 1

    Q1. Why does the 4s orbital fill before the 3d in potassium's electron configuration?

    • A) Lower energy due to penetration effects
    • B) Higher shielding from d-electrons
    • C) 4s has a larger capacity than 3d
    • D) Spin pairing energy dominates

    Answer: Lower energy due to penetration effects

    Explanation: Penetration lowers 4s energy (A). 3d has higher energy despite being in a lower shell (C is incorrect).