Electronegativity values

In a homonuclear diatomic molecule X2, the electron density in the region between the nuclei is symmetrical each X nucleus has the same effective nuclear charge. On the other hand, the disposition of electron density in the region between the two nuclei of a heteronuclear diatomic molecule X—Y may be asymmetrical. If the effective nuclear charge of Y is greater than that of X, the pair of electrons in the X—Y covalent bond will be drawn towards Y and away from X. 

Show that As in ASF3 obeys the octet rule. 

Draw Lewis stmctures for the following ions, ensuring that all atoms obey the octet rule (a) [NO] (b) [CN] (c) [AIH4]- (d) [NO2]-. 

however, not necessary to exceed a valence octet if we make use of charge-separated species as contributing resonance stmctures. In order to maintain the octet of electrons around the Cl centre in CIF3, we have to follow a similar strategy to that adopted in [NH4] described above (2.16). Whereas a Cl atom 3s 3p ) can form only one bond while obeying the octet mle, a Cl centre can form two bonds  

we can write a Lewis stmcture for CIF3 in terms of the charge-separated species 2.21. 

There is, however, a problem stmcture 2.21 implies that one Cl—F interaction is ionic, while the other two are covalent. This problem is readily overcome by drawing a set of three resonance stmctures  

---

Residual electronegativity values obtained by the PEOE method are useful quantitative measures of the inductive effect. 

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. 

Table. S.l Electronegativity values of some common elements...

Figure 2.2 Electronegativity values and trends. Electronegativity generally increases from left to right across the periodic table and decreases front top to bottom. The values are on an arbitrary scale, with F = 4.0 and Cs = 0.7. Elements in orange are the most electronegative, those in yellow are medium, and those in green are the least electronegative.

Probfem 2.3 Use the electronegativity values shown in Figure 2.2 to rank the following bonds I from least polar to most polar H3C — Li, H3C— K, H3C—F, H3C — MgBr, H3C—OH. 

Figure 1-3. Bond moments /i plotted against the difference in the original electronegativity values large circles represent bond moments for the bonds displayed in Figure 1-1.

Allred, A.L. Electronegativity Values from Thermochemical Data J. Inorg. Nucl. Chem. 1961, 17, 215-221. 

For several sets of electronegativity values, see Huheey, J.E. Inorganic Chemistry, 3rd ed. ... 

Any covalent bond between atoms of different elements is polar to some extent, because each element has a different effective nuclear charge. Each element has a characteristic ability to attract bonding electrons. This ability is called electronegativity and is symbolized by the Greek letter chi. When two elements have different electronegativity values, a bond between their atoms is polar, and the greater the difference (A. the more polar the bond. 

Use the periodic table, without looking up electronegativity values, to rank each set of three bonds from least polar to most polar (a) S—Cl, Te—Cl, Se—Cl and (b) C—S, C—O, C— F. 

The larger the difference in electronegativity, the more polar the bond. Therefore, we can use periodic trends in electronegativities to arrange these bonds in order of polarity. Electronegativities decrease down most columns and increase from left to right across the s and p blocks. Use the periodic table to compare electronegativity values and rank the bond polarities. 

You can use actual electronegativity values to verily that these rankings are correct. 

C09-0002. List in order of increasing polarity all the possible bonds formed from the following elements H, O, F. Consult Figure 9 for electronegativity values. 

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

Covalent radii and electronegativity values (Allred-Rochow) are abstracted from Huheey, J. E. Keiter, E. A. Keiter R. L. Inorganic Chemistry, 4th ed. Harper Row New York, 1993 pp. 187 and 292. 

Fig. 35. (a) Correlation between the photolysis rate of halomethyl-cobalamins and the electronegativity of the alkyl ligand. (The electronegativity values are shown as the sums of the Pauling electronegatives of the atoms attached to the methyl carbon.) (b) Correlation between pKa for displacement of benzimidazole and alkyl group electronegativity for a series of halomethyl-cobalamins... 

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

The pentafluorophenyl-group has an electronegativity value which has been estimated as being between that of chlorine and bromine so- 2). As would be expected, 3-pentafluorophenyltrifluorobenzyne (9) reacts with benzene to form the 1,4-cycloadduct in good yield 63>. 

If the competition data are compared with electronegativity values for the halogens 85>, then tetrafluorobenzyne is clearly in an anomalous position. The only reasonable explanation available at present is that tetrafluorobenzyne is so destabilized by the inductive effect of the fluorine atoms that it has lost a considerable amount of the selectivity which arynes normally show. Estimates for the heats of formation of the isomeric dichlorobenzynes and for tetrachlorobenzyne have recently been made from mass spectrometric studies and these do indicate a low stability for tetrachlorobenzyne 86>. Evidently more data are required for the tetrahalogenobenzynes. 

The coefficients a, b, and c (with a > 0, b > 0) for this charge dependence can be derived from the electronegativity values of a given atomic orbital in the neutral state, and in the positive and negative ions, which in turn are derived from the relevant IP s and EA s 37). Thus, the latter are the fundamental data on which the whole method is based. 

Fig. 23. Comparison between FMO-parameters and charge/electronegativity values. cu refers to the coefficient of orbital i at atom j...

The proton affinities (PA) of two restricted subsets of amines were correlated directly with inductive and polarizability effect parameters, respectively (Figs. 19 and 22). These can be combined with data on other hetero-substituted amines to give a set of 80 amines of different skeletal and substitution types (e.g. Fig. 24). In this and all other systems (below), a residual electronegativity value, %l2, (Eq. 5) derived from those of the atoms of the first, 1, and second, 2, sphere neighbors of the nitrogen atom is preferred as a measure of the inductive effect49). 

For OsF6 the absorption appears to increase steadily from near 23 kK. to the first maximum at 35.7 kK. and we therefore take this value for the first n - -t2g excitation a similar assignment is also adopted for the 40.8 kK. maximum. The optical electronegativity values derived thereform, and from a similar treatment of the IrF6 and PtFg spectra, are discussed in Section 5 (q.v.). 

---