Electronegativity Allred-Rochow scale

In this equation, Z is the effective nuclear charge, which takes into account the fact that an outer electron is screened from experiencing the effect of the actual nuclear charge by the electrons that are closer to the nucleus (see Section 2.4). In principle, the Allred-Rochow electronegativity scale is based on the electrostatic interaction between valence shell electrons and the nucleus. 

The first element, hydrogen, has an Allred Rochow electronegativity coefficient of 2.1, and an electronic configuration Is1. The atom may lose the single electron to become a proton, which exists in aqueous solutions as the hydroxonium ion, H30+(aq), in which the proton is covalently bonded to the oxygen atom of a water molecule. The ion is hydrated, as is discussed extensively in Chapter 2. The reduction of the hydrated proton by an electron forms the reference standard half-reaction for the scale of reduction potentials ... 

The relationship that gives Allred-Rochow electronegativities on the Pauling scale is... 

Several other approaches have been proposed for determining electronegativities but only two of these will be mentioned here. Mullikcn proposed an electronegativity scale based on taking x be the average of the E and Z values of the element. Allred and Rochow proposed that eleetronegativity be defined as the force exerted by the nucleus on the valence electrons,. so that the Allred-Rochow electronegativity. can be calculated from the... 

The quantity Z ff/r correlates well with Pauling electronegativities and the two scales can be made to coincide by expressing the Allred-Rochow electronegativity as... 

Covalent radii and electronegativity values from Ref. 10. AEN is the difference in electronegativity between the two elements using the Allred-Rochow scale. 

TABLE A.2. Comparison of Configuration Energy with Electronegativity Scales of Pauling t/P) and Allred and Rochow (/A E)°... 

Like the Mulliken method, the Allred-Rochow method defines electronegativities in terms of atomic rather than molecular properties. Another objection is that it fails in the case of hydrogen the above equation yields a value which would give H an electronegativity comparable with O. The value of 2.2 for hydrogen is rather arbitrarily chosen. Nevertheless, the Allred-Rochow scale has won widespread acceptance among inorganic chemists who find it consistent with many features of chemical periodicity. 

Allred and Rochow [i, ii] introduced their -> electronegativity scale. They defined the electronegativity of an element X ( R) as follows y1 1 = (35904s2 ) + 0.744 Zeff is the effective charge of the nucleus acting on the electron, and rcov is the covalent radius of the atom in pm. 

For example, fluorine has the Pauling electronegativity of 4.0 and a value of 3.91 on the Mulliken scale. A different approach was used by Allred and Rochow to establish an electronegativity scale. This scale is based on a consideration of the electrostatic force holding a valence shell electron in an atom of radius, r, by an effective nuclear charge,... 

A.L. ALLRED and E.G. ROCHOW, A scale of electronegativity based on electrostatic force. J. Inorg. Nucl. Chem., 5, 264 (1958). 

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