Ionic and Covalent Bonds

Atoms in a molecule are joined by bonds. Bonds are formed when the valence or outermost electrons of two or more atoms interact. The nature of the bond between atoms goes a long way toward determining the properties of the molecule. Chapter 5 introduced the two common types of chemical bonds covalent and ionic. Elements with similar electronegativities share electrons and form covalent bonds. But elements with greatly different electronegativities exchange one or more electrons. This is called an ionic bond. 

Both components yield the conserved overall bond index Af P) = 1 in the whole range of bond polarizations P e [0,1]. Therefore, this model properly accounts for the competition between the bond covalency and ionicity, while... 

As we have already mentioned in Section 2, in OCT the complementary quantities characterizing the average noise (conditional entropy of the channel output given input) and the information flow (mutual information in the channel output and input) in the diatomic communication system defined by the conditional AO probabilities of Eq. (48) provide the overall descriptors of the fragment bond covalency and ionicity, respectively. Both molecular and promolecular reference (input) probability distributions have been used in the past to determine the information index characterizing the displacement (ionicity) aspect of the system chemical bonds [9, 46-48]. 

According to Eq. (4-29), protons can be transferred from Bronsted acids A—H to bases B via the hydrogen-bonded covalent and ionic complexes (a) and (b), depending on both the relative acidity and basic strength of A—H and B, respectively, and the solvation capability of the surrounding medium [265, 266]. Eq. (4-29) is simplified because not only 1 1 complexes but 1 2 and higher complexes can be formed in solution. 

Chemical bonds are strong forces of attraction which hold atoms together in a molecule. There are two main types of chemical bonds, viz. covalent and ionic bonds. In both cases there is a shift in the distribution of electrons such that the atoms in the molecule adopt the electronic configuration of inert gases. 

Potassium methoxide, KOCH3, contains both covalent and ionic bonds. Which do you think is which ... 

They have a complex electronic bonding system which includes metallic, covalent, and ionic components. 

It has to date been recognized that the breaking and forming of bonds in solution are in principle influenced by three major factors electronic, steric and solvent effects. Thus, in a quantitative examination to differentiate covalent and ionic bond formation, it is necessary first to investigate the electronic effect alone, separate from steric and solvent effects. 

It should be clear by now that inorganic solids (which consist of atoms bound together by both covalent and ionic forces) do not react by either changing the bonding within a molecular structure or by reacting one-on-one in a mobile phase such as a liquid, as do orgeuiic compounds. Solids can only react at the interfiace of another solid, or in the case of a liquid-solid reaction, react with the liquid molecule at the solid interface. 

The most fundamental issues of the structures of heavier group 14 element-centered anionic derivatives R3EM (R = alkyl, aryl, silyl E = Si, Ge, Sn, Pb M = alkali or alkaline earth metals) turned out to be the questions of their aggregation states (monomeric, dimeric, or oligomeric), nature of the E-M bond (covalent or ionic), and configuration of the anionic centers E (tetrahedral, pyramidal, or planar). The most important experimental techniques that are widely used to clarify these questions are NMR spectroscopy and X-ray diffraction analysis. 

Lewis considered covalent and ionic bonds to be two extremes of the same general type of bond in which an electron pair is shared between two atoms contributing to the valence shell of both the bonded atoms. In other words, in writing his structures Lewis took no account of the polarity of bonds. As we will see much of the subsequent controversy concerning hypervalent molecules has arisen because of attempts to describe polar bonds in terms of Lewis structures. 

The hardness of A1203 is VHN = 2700kg/mm2 and its rms. shear stiffness is 366 GPa so its Chin-Gilman parameter is 0.074. This suggests that its chemical bonding is a combination of covalent and ionic bonding. 

The terms covalent and ionic bonding represent the extremes of the bond types. In reality, the bonding in most compounds is intermediate between the two extremes. 

Table 3.30. The NRTdescriptors of XYZ triatomic anions (see Table 3.28), showing bond orders (bxy and by/), central-atom valency (Vy total, covalent, and ionic components), and percentage weights of leading resonance structures (X—Y Z, X. Y— Z, X—Y— Z, X. Y+ Z )...

The empirical valence bond (EVB) method of Warshel [19] has features of both the structurally and thermodynamically coupled QM/MM method. In the EVB method the different states of the process studied are described in terms of relevant covalent and ionic resonance structures. The potential energy surface of the QM system is calibrated to reproduce the known experimental... 

Calculated assuming covalent and ionic contributions to bonding are in the ratio l/X of the charge derived from dipole moments (152). 

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