What Does Hund's Rule Mean?
Hund's rule states that a larger total spin state of an atom sometimes makes the atom more stable. This rule is fairly reliable (with occasional failures) for the determination of the state of a given excited electron configuration. It was discovered in the year 1925 by Friedrich Hund. According to Hund's rule:
- Each orbital in a sublevel is separately occupied before any orbital is doubly occupied.
- All of the electrons in separately occupied orbitals have an equivalent spin (to maximize total spin).
Hund's rule is also known as the Rule of Maximum Multiplicity.
Electrons always enter an empty orbital before they pair up, according to the first rule. Electrons repel each other as a result of their negative charge. Electrons, rather than sharing an orbital with another electron, will occupy their own in order to minimize repulsion. Quantum-mechanical calculations have shown that electrons in singly occupied orbitals are less effectively shielded from the nucleus.
According to the second rule, electrons in singly occupied orbitals that are unpaired have the same amount of spins. The first electron in a sublevel could either "spin-up" or "spin-down." However, once the spin of the first electron that is in a sublevel has been chosen, the spins of all other electrons in that sublevel are dependent on that first spin.