Mullikenschaal

Mullikenschaal, or the Mulliken electronegativity scale, is a method for assigning a numerical value to an atom’s tendency to attract electrons in a chemical bond. It was proposed by Robert S. Mulliken in the 1930s as a way to quantify electronegativity using physical atomic properties.

The scale defines electronegativity as the average of the first ionization energy (I) and the electron affinity (A) of an atom: χ_M = (I + A)/2, with both I and A expressed in electronvolts (eV). Values pertain to isolated gas-phase atoms; for noble gases, electron affinity is small or negative, which affects their χ_M values accordingly.

The Mulliken scale is conceptually linked to other electronegativity scales, such as the Pauling scale, but it relies on physical energy quantities rather than a dimensionless bond scale. There is a general positive correlation between higher Mulliken values and greater bond polarity, yet the relationship between scales is not strictly linear. Today the Mulliken approach is less widely used in routine computational work, partly due to data availability and the influence of an atom’s environment on observed values.

Typical electronegativity values (in eV) include: H ≈ 7.18, Li ≈ 3.00, C ≈ 6.26, O ≈ 7.54, F ≈ 10.41. These figures reflect the underlying data for ionization energies and electron affinities and illustrate the scale’s broad range across the periodic table.

See also: electronegativity scales, Pauling scale, ionization energy, electron affinity.