Electronegativity relating bond types

Compare the physical properties of substances that have different bond types, and relate bond types to electronegativity differences. 

Related topics Electronegativity and bond type (Bl) Methods of characterization (B7) ... 

Relating bond type to electronegativity difference between atoms. 

The phosphonitrilic halides are weaker bases than are some related nonaromatic compounds, just as pyridine is a weaker base than piperidine. The bond type in the phosphonitrilic series is probably the same as in the phosphine-imines RaPrNR (80, 81) the stability of these compounds, too, increases with the electronegativity of the substituents on the phosphorus. Tetraphenylphosphine-imine is one of the most stable of these compounds, and forms a hydrochloride. Its base strength is therefore greater than those of the phosphonitrilic halides, presumably because the opportunities for electronic delocalization are less. The Af-ethyl ester of the trimeric phosphonitrilic acid, which has a cyclic structure, but in which resonance of the same type as in the phosphonitrilic halides cannot occur, also forms a hydrochloride ( 1). It is, therefore, a comparatively strong base, in spite of the inductive effect of the two oxygen atoms on the phosphorus. The extreme weakness of the phosphonitrilic halides as bases cannot therefore be wholly due to the inductive effect of the halogens. 

The third type of monomer pair is that which shows an alternating tendency. This tendency is related to the polarization properties of the monomer substituents [73]. Monomers that are dissimilar in polarity tend to form alternating monomer sequences in the polymer chain. An example is the monomer pair acrylonitrile-styrene, with Ri = 0.07 and i 2 = 0-37, with corresponding component rate constants shown in Table 12.7. Styrene, with its pendant phenyl group, has a relatively electronegative double bond, while acrylonitrile, with its electron-withdrawing nitrile group, tends to be electropositive. 

Electronegativities are used to predict bond type. The greater the difference in electronegativity between two atoms (Ax) the greater the ionic character (/) of a bond between them is expected to be. Several different relations between / and Ax have been proposed. A simple one is... 

A FIGURE 10.6 The continuum of bond types The type of bond (pure covalent, polar covalent, or ionic) is related to the electronegativity difference between the bonded atoms. 

Fluorocarbons, hydrocarbons, and silicones exhibit widely differing cohesive energies as a result of the different natures of the C-C-F, Si-C-H, and C-C-H bonds. Those differences are a reflection of differences in the electronegativities of the various bond types. Surface energies and surface tensions can be related to those cohesive energy parameters. Liquids having the same number of carbon atoms show decreasing surface tensions in the order hydrocarbons > silicones > fluorocarbons. 

Another type of correction, which is related to cross terms, is the modification of parameters based on atoms not directly involved in the interaction described by the parameter. Carbon-carbon bond lengths, for example, become shorter if there are electronegative atoms present at either end. Such electronegativity effects may be modelled by adding a correction to the natural bond length based on the atoms which are attached to the A-B bond. 

An attractive feature of applying XPS to study these skutterudites is that the valence states of all atoms can be accessed during the same experiment. As in the study of the MnP-type compounds, these types of investigations also provide insight into bonding character and its relation to electronegativity differences. This information is obtained by analysing both core-line and valence band XPS spectra. 

Electronegativity is the tendency of an atom to attract electrons and is related to electron affinity. The electronegativity difference between two bonded atoms is used to determine the type of bond that most likely occurs. 

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