AllredRochow

AllredRochow refers to the Allred–Rochow electronegativity scale, a method introduced in 1958 by chemists Allred and Rochow for assigning a numerical value to an element's electronegativity. The scale estimates electronegativity from the effective nuclear charge Z_eff experienced by the atom's valence electrons, with Z_eff calculated using Slater's rules. After computing Z_eff, the values are calibrated to match observed chemical trends, yielding a scale where higher values indicate greater electronegativity.

The Allred–Rochow scale was developed as an alternative or complement to more widely used scales such as the Pauling scale. It emphasizes the link between electronegativity and core shielding, and it often correlates with properties such as ionization energy and covalent radii. The method is most straightforward for main-group elements; for transition metals and heavier elements, the estimates can be less reliable due to relativistic effects and electron correlation.

In modern usage, the Allred–Rochow scale is mostly of historical and pedagogical interest. It is documented in chemical handbooks and used to illustrate how effective nuclear charge relates to bond polarity, though it is not as widely employed in current research as the Pauling or Mulliken scales.

See also: electronegativity, Slater's rules, Pauling scale, Mulliken scale.