Allred and Rochow

Later methods, especially that of Gordy (1955), and later Allred and Rochow (1958) make use of screening constants of the electron strucmre for the nuclear charge of each atom. This determines die attraction between the nucleus of the atom and an electron outside the normal electron complement, and is die effective nuclear charge. The empirical equation for the values of electronegativity obtained in this manner by Allred and Rochow is... 

Table 1.2 Electronegativity Values According to Allred and Rochow...

If a property is as important as is electronegativity, it is not surprising that a large number of approaches have been taken to provide measures of the property. Although we have already described two approaches, we should also mention one additional method. Allred and Rochow made use of the equation... 

Fe3+. There are several ways of defining electronegativity, the simplest being that of Allred and Rochow (1958), which calculates the force experienced by the outer electron from the nucleus using Coulomb s law of electrical attraction ... 

The binding of a metal ion to a ligand can be considered in terms of Lewis acid-base theory (Lewis, 1923 Allred and Rochow, 1958 Brown and Skowron, 1990) because, in accepting an electronic pair, the metal ion acts as a Lewis acid. When a metal ion coordinates a ligand, it can affect the electron distribution of the ligand and therefore its reactivity. 

The now generally accepted scale of electronegativity was derived by Allred and Rochow and is known by their names. It is based on the concept that the electronegativity of an element is related to the force of attraction experienced by an electron at a distance from the nucleus equal to the covalent radius of the particular atom. 

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

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,... 

The empirical method of Allred and Rochow [121] models electronegativity as the force acting on atomic electrons at the distance of the covalent radius,... 

Bectronegativities. Xar- shown in normal typeface are calculated using the Allred-Rochow method and are taken from Allred and Rochow or from Little and Jones. ... 

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... 

Other scales have been proposed, namely by Allred and Rochow, in 1958 (ref. 75), and by Allen, in 1989 (ref. 76). In the first case, the electronegativity, xarj is an atomic property taken proportional to the force exerted by the effective nuclear charge at the periphery of the atom ... 

Allred and Rochow counted a//of the electrons in a particular atom a.s shielding the electron coming from another atom, so their Z values arc 0.35 higher than those obtained by the usual application of Slater s rules. Such differences are unimportant as long as one is consistent in the application They will be absorbed into the appropriate parameters for fitting Eq. 5.82. 

Electronegativity scales, table, 238 Allred and Rochow, 238 configuration energy, 238 Pauling, 238... 

In the scale of Allred and Rochow, electronegativity is measured as the electrostatic force exerted at the covalent radius (rcov) of the atom [14,15]. This electronegativity can be written as a function of the screened nuclear charge (Z ) and the atomic size as ... 

The major advantage in the definition of Allred and Rochow is that it provides a direct physical interpretation of electronegativity as the electron-attracting power of atoms. ... 

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