Question

Why does praseodymium possess electronic configuration 4f³ 6s² instead of the expected one, 4f² 5d¹ 6s²?

Answer 1

1. Energy considerations: The 4f-orbitals in lanthanoids decrease in energy as electrons are added, becoming more stable than the 5d orbital.
2. The additional electron enters the 4f orbital rather than the 5d, resulting in a 4f³ 6s² configuration.
3. This pattern continues until the 4f subshell is half-filled or fully filled, due to the increased stability of these configurations.

Hence, praseodymium prefers 4f³ 6s², not 4f² 5d¹ 6s², due to the lower energy and greater stability of electrons in 4f orbitals.