The ground state of an atom corresponds to the state when all electrons occupy the lowest energies. Besides the rules we discussed in the lecture, the subshell with half-filled or fullfilled electrons possesses a lower energy state. Based on this rule, we can explain some transition metals like Cr (Z = 24) and Cu (Z = 29).

(a) (10 marks) Please show the electron configurations for atom Cu and Cr.

(b) (10 marks) How many valence electrons do Cu and Cr have?

(c) (5 marks) What are the possible quantum numbers of all valence electrons of Cr?