MDCAT Chemistry MCQ #977

A student writes the electron configuration of copper as [Ar] 3d9 4s2. Why is this incorrect?

MDCAT Chemistry MCQ #977

  1. Question 1

    Q1. A student writes the electron configuration of copper as [Ar] 3d9 4s2. Why is this incorrect?

    • A) 3d orbitals fill before 4s
    • B) Copper has a stable 3d10 configuration
    • C) Pauli exclusion principle violation
    • D) Invalid azimuthal quantum numbers

    Answer: Copper has a stable 3d10 configuration

    Explanation: Copper prefers fully filled 3d subshell ([Ar] 3d10 4s1) for extra stability. Options A/C/D ignore this exception.