Which of the following best explains why the electron configuration of the ion is…

CHEMISTRY · Single correct · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties

Problem

Which of the following best explains why the electron configuration of the

\text{Cu}^+

ion is

[\text{Ar}]\,3d^{10}

rather than

[\text{Ar}]\,3d^{9}\,4s^{1}

? (a) Electrons are always removed from the subshell that was filled last, which for copper is the

3d

subshell, so a

3d

electron is lost. (b) Because the

4s

subshell has the higher principal quantum number (

n=4

), it lies closer to the nucleus and is lower in energy than

3d

, so the ion loses a

3d

electron instead. (c) A completely filled

3d

subshell is lower in energy than a

4s

electron, so losing the

4s

electron yields a more stable arrangement. (d) Removing a

3d

electron would leave the

3d

subshell half-filled, and half-filled subshells are most stable, so the ion prefers the

[\text{Ar}]\,3d^{9}\,4s^{1}

configuration.