Tuesday, February 4, 2014

This Day in Science History - February 4 - Friedrich Hund and Hund's Rule

February 4th is Friedrich Hund's birthday. Hund was a German physicist who introduced a method to use molecular orbitals to determine electron structure of molecules and bonds. Hund's rules are a set of rules that determine the ground state of a multi-electron atom based on the energy levels of the filled orbitals.

Hund proposed a set of three rules electrons follow to fill up "shells" or orbitals in multiple electron atoms. In chemistry, only one rule is generally referred to as "Hund's Rule". This rule comes in to play when determining the electron configuration of an atom and the Aufbau principle. Hund's rule deals with the quantum number dealing with spin, s. The s quantum number has two possible values, +½ and -½, also known as "spin up" and "spin down". The rule states that in an orbital, electrons will fill all available positions of the same value of s before the opposite spin value appears.

Determining an atom or molecule's electronic structure can give useful insight as to how the atom or molecule will combine with other molecules or atoms.

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