Electronegativity scales, table

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

The current chemistry of the Group IV elements has been reviewed in the second volume of the MTP series. In an analysis of the i.r. band intensities of a number of MHCI3 and MX4 (M = C, Si, or Ge X = F, Cl, Br, or I) molecules, the electronegativities of the Group IV elements have been shown not to vary smoothly as deduced by Pauling, but to vary erratically, as indicated by the Allred-Rochow and Sanderson Electronegativity scales (Table 1). 

An estimate of the polarity of a bond between two atoms may be obtained by reference to the electronegativity scale. The electronegativity values of some common elements are given in Table 5.1. The higher the value the greater the electronegativity. 

On the basis of this equation, systematically considering all the available thermochemical data and arbitrarily assigning to the most electronegative element, fluorine, a value of about 4, Pauling was able to prepare a complete electronegativity scale. This is shown in Table 2.1. 

Carbon occupies an intermediate position in the electronegativity scale (with a value of 2.5) and forms covalent bonds with neighbouring elements in the Periodic Table. 

An obvious use of an electronegativity scale is to predict the direction of electrical polarity of a covalent bond with ionic character. Table 2.2 tells us that the C—H bond in alkanes (CnH2n+2) is polar in the same sense as the 0—H bonds in water, although to a much lesser degree ... 

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

Table 14. The electronegativity scale of the rare earths [217] and the coefficients of Eq. (18)...

However, many covalent bonds do not equally share electrons such covalent bonds, as pointed out above, are referred to as polar covalent bonds or bonds of partial ionic character. Electronegativity is rated on a relative scale ranging from 4 (most electronegative, fluorine) to 0.7 (least electronegative, cesium) (Table 1.7). In general, the greater the difference in electronegativity between two elements, the more ionic will be the bond between them (Fig. 1.2). 

Mulliken has arrived at an electronegativity scale by another and better way, obtaining good agreement with that of Pauling (Table 15). 

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