The Azimuthal quantum number for the valence electrons of Ga⁺ ion is ___________.
(Atomic number of Ga = 31)

Solution

Chemistry ma’am · 4 steps

Take the electron away first, then see which subshell is left on the outside.

1. Neutral Ga. Gallium has 31 electrons: Ga is [Ar] 3d¹⁰ 4s² 4p¹. The outermost shell is n = 4.
2. Form the ion. An atom loses electrons from its highest-energy outer subshell first. Here that is the single 4p electron, so Ga⁺ is [Ar] 3d¹⁰ 4s².
3. Read off l. The valence electrons of Ga⁺ are now the two 4s electrons. For an s subshell the azimuthal quantum number is l = 0 (s = 0, p = 1, d = 2, f = 3).
4. So. The azimuthal quantum number of the valence electrons of Ga⁺ is 0.

The common slip: 1. Using the 4p electron of neutral Ga gives l = 1, but that electron is the one removed when Ga⁺ forms.

The idea to keep. For an ion, write the neutral atom's configuration, remove electrons from the outermost subshell, and only then ask which subshell holds the valence electrons.

Answer from the NTA final answer key. Solution by PrepWiser.