electron configuration of ions, q 3.5 [ENDORSED]

[Lindsay H 2B]

can anybody explain why according to the solutions manual, in question 3.5 the ground-state electron configuration from Ga^3+ is [Ar]3d^10 instead of [Ar]3d^8 4s^2, and also why the ground-state configuration for Tl is [Xe]4f^14 5d^10 instead of [Xe]4f^14 5d^8 6s^2?

[Lindsay H 2B]

***typo, it's Ga^3+ and Tl^3+; sorry!!

[Nancy Dinh 2J]

can anybody explain why according to the solutions manual, in question 3.5 the ground-state electron configuration from Ga^3+ is [Ar]3d^10 instead of [Ar]3d^8 4s^2, and also why the ground-state configuration for Tl^3+ is [Xe]4f^14 5d^10 instead of [Xe]4f^14 5d^8 6s^2?

The ground state for the neutral elements are:
Ga --> [Ar] 3d^10 4s^2 4p^1
Tl --> [Xe] 4f^14 5d^10 6s^2 6p^1

Remember that when you take away valence electrons, you take away from the outermost orbital of the outermost shell. In the case of Ga, the three outermost valence electrons are from the 4s and 4p orbital. Once you removes these electrons, you will get Ga^3+ = [Ar] 3d^10. Likewise, the three outermost valence electrons for Tl are in the 6s and 6p orbitals, so the resulting ion will be Tl^3+ = [Xe]4f^14 5d^10.