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Hund's Rule

Definition - 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.

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).

This rule is fairly reliable (with occasional failures) for the determination of the state of a given excited electronic configuration.

Hund's rule is also known as the rule of maximum multiplicity.

Corrosionpedia explains Hund's Rule

According to Hund's rule, electrons are placed into separate orbitals before going into an orbital this is already occupied. This can help predict the properties of atoms, as paired and unmated electrons have distinct properties (specifically with interactions with magnetic fields).

Since electrons are negatively charged, they repel each other. Electrons tend to attenuate repulsion by occupying their own orbitals, instead of sharing an orbital with another electron. For the second rule, unmated electrons in separately occupied orbitals have an equivalent spins. The primary electron in a sublevel could be either "spin-up" or "spin-down."

When atoms come into contact with each other, the outer electrons of those atoms, or valence shell, initially interact. An associate atom is least stable (and therefore most reactive) when its valence shell is not full. The valence electrons are most responsible for an associate element's chemical behavior. Parts that have an equivalent range of valence electrons typically have similar chemical properties.

An associate atom is most stable (and therefore unreactive) once all its orbitals are full of electrons. These configurations are found in the noble gases, which are extremely stable and do not normally react with each other.

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