Difference in electronegativity

The greater the difference in electronegativity, the greater is the ionic character of the bond. The amount of ionic character I is given by ... 

This dispersion interaction must be added to the dipole-dipole interactions between molecules, such as HCl, NH3 and H2O which have a permanent dipole, fi. The magnitude of die dipole moment depends on tire differences in electronegativity of the atoms in the molecule. Here again, the energy of interaction varies as (orientation effect). 

The dipole moment of a molecule is another additive property since it arises from the difference in electronegativity of two atoms connected by a double bond. It should therefore be possible to associate a dipole moment with every linkage. Eucken and Meyer" have suggested the following moments for various linkages (in units of 10 e.s.cm)... 

The bond dipoles in Table 1.3 depend on the difference in electronegativity of the bonded atoms and on the bond distance. The polarity of a C—FI bond is relatively low substantially less than a C—O bond, for example. Don t lose sight of an even more important difference between a C—FI bond and a C—O bond, and that is the direction of the dipole moment. In a C—FI bond the electrons are drawn away from FI, toward C. In a C—O bond, electrons are drawn from C toward O. As we ll see in later chapters, the kinds of reactions that a substance undergoes can often be related to the size and direction of key bond dipoles. 

When two atoms that differ in electronegativity are covalently bonded, the electrons in the bond are drawn toward the more electronegative element. 

Which is more important, the difference in electronegativity between the bonded halogens or the length of the bond between them [Remember that the dipole moment depends on both charge and distance (p. = e X d).]... 

Next, examine electrostatic potential maps for the same set of compounds. Focus your attention on the value of the potential around hydrogen. For which molecule is it most positive For which is it most negative Is there a correlation between the value of the potential and the difference in electronegativities Plot charge on hydrogen (vertical axis) vs. difference in electronegativities (horizontal axis). Is there a correlation ... 

A covalent bond will exhibit polarity when it is formed from atoms that differ in electronegativity, i.e., the ability to attract electrons. The order of electronegativity of some elements [50, p. 16] is... 

Most organic compounds are electrically neutral they have no net charge, either positive or negative. We saw in Section 2.1, however, that certain bonds within a molecule, particularly the bonds in functional groups, are polar. Bond polarity is a consequence of an unsymmetrical electron distribution in a bond and is due to the difference in electronegativity of the bonded atoms. 

The extent of polarity of a covalent bond is related to the difference in electronegativities of the bonded atoms. If this difference is large, as in HF (AEN = 1.8), the bond is strongly polar. Where the difference is small, as in H—C (AEN = 0.3), the bond is only slightly polar. 

Table IV presents the results of the determination of polyethylene radioactivity after the decomposition of the active bonds in one-component catalysts by methanol, labeled in different positions. In the case of TiCU (169) and the catalyst Cr -CjHsU/SiCU (8, 140) in the initial state the insertion of tritium of the alcohol hydroxyl group into the polymer corresponds to the expected polarization of the metal-carbon bond determined by the difference in electronegativity of these elements. The decomposition of active bonds in this case seems to follow the scheme (25) (see Section V). But in the case of the chromium oxide catalyst and the catalyst obtained by hydrogen reduction of the supported chromium ir-allyl complexes (ir-allyl ligands being removed from the active center) (140) C14 of the...

Electronegativity is a measure of the pulling power of an atom on the electrons in a bond. A polar covalent bond is a bond between two atoms with partial electric charges arising from their difference in electronegativity. The presence of partial charges gives rise to an electric dipole moment. 

FIGURE 2.13 The dependence of the percentage ionic character of the bond on the difference in electronegativity, A, between two bonded atoms for a number of halides. 

In the above discussion the effect of difference in electronegativity of unlike atoms on bond length (usually a decrease) has been ignored. There is the possibility also of a small change in bond length between unlike atoms, such as of a metal and a metalloid, that reflects the difference in the nature of the overlapping orbitals, in addition to the effects of partial ionic character and of electron transfer. I believe that a thorough... 

When the difference in electronegativities is great, the orbital may be so far over to one side that it barely covers the other nucleus. This is an ionic bond, which is seen to arise naturally out of the previous discussion, leaving us with basically only one type of bond in organic molecules. Most bonds can be considered intermediate between ionic and covalent. We speak of percent ionic character of a bond, which indicates the extent of electron-cloud distortion. There is a continuous gradation from ionic to covalent bonds. 

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. 

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