Scales Of Electronegativity, Pauling, Mulliken And Allred-Rochow, Important Topics For JEE 2024

Scales Of Electronegativity : Electronegativity, a concept central to understanding chemical bonding and reactivity, quantifies the ability of an atom to attract shared electrons in a chemical bond. The development of electronegativity scales has been crucial in providing a quantitative framework for analyzing and predicting various chemical phenomena. Among the notable scales are those proposed by Linus Pauling, Robert S. Mulliken, and J. Allred and E. Rochow.

Each scale offers a unique approach to measuring electronegativity, considering factors such as chemical behaviour, ionization energy, electron affinity, effective nuclear charge, and atomic radius. These scales provide valuable insights into the nature of chemical bonds, molecular structures, and intermolecular interactions, thereby facilitating advancements in chemistry across diverse research fields. This article explores the significance of the Pauling, Mulliken, and Allred-Rochow scales of electronegativity, elucidating their contributions to the understanding of chemical phenomena.

Pauling Electronegativity Scale: Proposed by Linus Pauling, this scale assigns electronegativity values to elements based on their chemical behaviour and bond energies. The Pauling electronegativity values range from approximately 0.7 for cesium (Cs) to 4.0 for fluorine (F), with fluorine being the most electronegative element.

EN was explained by Pauling for the first time

Electronegativity of some other elements are as follows:

Mulliken Electronegativity Scale

Mulliken Electronegativity Scale : Developed by Robert S. Mulliken, this scale calculates electronegativity values based on the average ionization energy and electron affinity of an atom. The Mulliken electronegativity values are similar to the Pauling scale but may differ for certain elements.

• According to Mulliken, electronegativity is the average value of ionisation potential and electron affinity of an element;

X _p = Pauling’s EN Where (EN = electronegativity)

X _m = Mulliken’s EN

• If ionization potential and electron affinity are given in eV, then electronegativity by Mulliken on Pauling scale will be

• If ionization potential and electron affinity are given K.cal/mole then;

Allred-Rochow Electronegativity Scale

Allred-Rochow Electronegativity Scale : Proposed by J. Allred and E. Rochow, this scale considers the effective nuclear charge and atomic radius of an atom to determine its electronegativity. The Allred-Rochow electronegativity values correlate closely with chemical properties and are used particularly in predicting bond strengths.

The electronegativity of an element is the electrostatic force of attraction between the electron present on the circumference of the outermost shell of this atom and the atomic nucleus. If the distance between the circumference of outermost shell & the nucleus is r and the effective nuclear charge Z _eff then -

Z = The actual number of charge present in the nucleus i.e., number of proton and σ = shielding constant.

Important Note : (1) Z _eff to be calculated for (x + 1) ^th valence