MullikenSkala

The Mulliken scale, also known as Mulliken electronegativity, is a scale used to quantify the tendency of an element to attract electrons. It was introduced by Robert S. Mulliken in the 1930s and defines electronegativity as the average of the first ionization energy and the first electron affinity of an isolated atom. The formal expression is χ_M = (I + A)/2, where I is the first ionization energy and A is the electron affinity. Values are commonly expressed in electronvolts (eV).

In practice, I and A are measured for gaseous atoms, giving a physical basis for the scale. For example, hydrogen has I ≈ 13.6 eV and A ≈ 0.754 eV, yielding χ_M ≈ 7.2 eV; fluorine has I ≈ 17.4 eV and A ≈ 3.4 eV, yielding χ_M ≈ 10.4 eV. The Mulliken scale provides a comparative, intrinsic measure of an element’s ability to attract electrons, and tends to correlate with other electronegativity scales, though the numerical values are not directly interchangeable with, for instance, the dimensionless Pauling scale.

Limitations include the dependence on ionization energies and electron affinities, which are not always well-defined for all elements (notably some noble gases). Consequently, the Mulliken scale is most reliable as a qualitative or semi-quantitative tool for trends and theoretical considerations in inorganic and physical chemistry.

See also: electronegativity scales, Mulliken population analysis, Allred–Rochow scale, Pauling scale.