Question

Explain Hund's rule and electronic configuration?

Answer 1

Hund's rule

• Before any orbital is doubly occupied, all orbitals in the sub-level are singly occupied.
• All electrons in a single-occupancy orbital have the same spin in order to maximize overall spin.
• An electron can fill all of its orbitals with the same energy, therefore it won't couple with another electron in an orbital that is only partially filled.
• Atoms in their ground state have a lot of unpaired electrons.
• The behavior of two electrons in contact would be similar to that of two magnets.

Electronic configuration

• According to Hund's maximum multiplicity rule, all electrons entering a subshell fill the subshell's orbitals singly, i.e. unpaired electrons occupy all orbitals first.
• To maximize the multiplicity of spin, all such electrons have the same spin.
• According to the rule, the lowest energy term in the electronic configuration will have the highest spin multiplicity value.
• An atom's electronic configuration in its stable state has a maximum number of electrons.
• Electrons can only share an orbital once all degenerate orbitals have been filled with electrons of the same spin.
• When electrons enter $p$-subshells, all three $p$-orbitals will have one each, and only the fourth, fifth, and sixth electrons will be able to share the orbitals that are already occupied.
• Example: Carbon with atomic number $6$, hence its electronic configuration is $1s^{2}2s^{2}2p^2$.