Obtain the valence-shell configuration of the thallium atom, Tl.?

Question

Obtain the valence-shell configuration of the thallium atom, Tl, using the position of this atom in the periodic table.

Answer 1

It's in the 6th row, so n= 6.
It's in the first column of the "p" block of the table, so it's highest energy electron is 6p1

Starting from Xe, and following the atomic numbers, these are the orbitals that are filled :

[Xe] 6s2 4f14 5d10 6p1

The valence electrons are the ones with the highest quantum numbers: 6s2 6p1.