Covalent bond with ionic character

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 ... 

Polar covalent bonds are covalent bonds with ionic character (partial election transfer). Ionic and covalent bonding are extremes forms of bonding polar bonds are intermediate in nature. The larger the difference in electronegativity between the atoms, the greater the polarity of the... 

In the case of heteronuclear diatomics there may be large differences in electronegativity, causing deviation from pure covalent interaction, either as dative bonds or ionic contribution to the bonding. Bonding plots, based on experimental measurement, are expected to distinguish between essentially covalent interactions and bonds with ionic character. This distinction is made obvious in Figures 5.6(c) and 5.6(d). 

The transition from pure covalent bonds over polar covalent bonds to ionic bonds is fluent as described in the section 2.1.1 Bond types. In this section we are going to look at bonds with ionic character. We are also... 

It is customary to use the line between two atomic symbols, A—B, to represent a normal covalent bond, with the usual amount of ionic character. In the discussion that follows, A B is used to represent a pure covalent single bond, and A+B to represent the ionic structure that is hybridized with A B to give A—B. A pure covalent double bond is represented by A=B. Thus in the molecule NF3 we might describe each NF bond as involving N+ F , N F , and N F +, that is, as having some covalent double-bond character. 

Because the Cl atom is more electronegative than the H atom, the bond pair is pulled towards the Cl atom. This results in a covalent bond with some partial ionic character the small charges present are indicated by a 8. 

Instead of using this description of the bond as involving resonance between an extreme covalent bond H C1 and an extreme ionic bond H+Cl-, we may describe the bond as a covalent bond with partial ionic character, and make use of the valence line, writing H—Cl (or H—Cl )... 

In all of the molecules discussed above the bond is intermediate between theeovalent extreme M X and the ionic extreme M+X , varying from an essentially covalent bond with only a small amount of ionic character (hydrogen iodide), through a bond with about equal amounts of covalent and ionic character (hydrogen fluoride), to an essentially ionic bond with only a small amount of covalent character (cesium chloride). 

The Third-Group Elements.—The B—F bond has about 63 percent ionic character, B—O 44 percent, B—Cl 22 percent, and so forth. Bor,on forms normal covalent bonds with hydrogen. The aluminum bonds are similar to those of beryllium in ionic character. 

These covalent radii are for use in molecules in which the atoms form covalent bonds to a number determined by their positions in the periodic table—carbon four, nitrogen three, and so on. It is found empirically that the radii are applicable to covalent bonds with considerable ionic character for extreme ionic bonds, however, ionic radii are to be used (Chap. 13), and in some molecules, discussed in later sections, the partial ionic character plays an important part in determining the interatomic distances. 

In all of these crystals it is probable that the bonds are covalent bonds with some ionic character. In ZnS, for example, the extreme covalent structure... 

In these structures the formation of a double covalent bond with one oxygen atom may be correlated with the ionic aspect of the bond to another atom, so that the bond orbitals used by the sulfur atom have the normal p nature (with only the usual small amount of d and s character—Chap. 4) come use may also be made of the 3d orbitals, In sp d or sp

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In crystalline substances, arsenic forms covalent bonds with itself and most other elements. That is, an arsenic atom in a covalent bond shares its valence electrons with another atom in the bond. However, unless arsenic atoms bond to each other, the valence electrons in a covalent bond are not equally shared between the arsenic atom and the atom of the other element. That is, most of the covalent bonds still have an ionic character to them (Faure, 1998), 83-89. 

Finally, other factors, including the increased covalent bonding with bridging oxygen atoms in the amphibole M4 and pyroxene M2 sites and the slightly larger ionic character of the olivine Ml site, also influence distributions of the cations in coexisting minerals. 

Some covalent bonds with slight ionic character... 

Often only the covalent structure is shown, and the chemist bears in mind that the covalent bonds have a certain amount of ionic char acter. These bonds are called covalent bonds with partial ionic character. 

Deviations from the Octet Rule. Sometimes heavy atoms form so many covalent bonds as to surround themselves with more than four electron pairs. An example is phosphorus pentachloride, PCl in the molecule of this substance the phosphorus atom is surrounded by five chlorine atoms, with each of which it forms a covalent bond (with some ionic character). 

The percent ionicity (ionic character) is related to the difference between the EN values of the atoms of the C-Met bond (ENc-EN gJ. These are estimated values, which are affected by the nature of the substituents on carbon. Nevertheless, they indicate that the C-Li, C-Mg, C-Ti, and C-Al bonds are more ionic than C—Zn, C-Cu, C-Sn, and C-B, which form mainly covalent bonds with carbon. Manipulation of certain organometallic reagents requires special techniques. ... 

The coefficients of ij/i and i/ n the composite description are equal, indicating that these two contribute equally to the structure. The coefficient of differs from the other two, indicating that i/ ni contributes differently. The contributions of the three structures in HCl are estimated to have the values I, 26 % II, 26 % III, 48 %. The structures I and II are covalent structures, so we may say that the bond in HCl is 52 % covalent and 48 % ionic. A bond in which the ionic contribution is significant is called a covalent bond with partial ionic character. 

The relationship between the ionic character of a covalent bond and the electronegativity difference of the bonded atoms. Note that the compounds with ionic character greater than 50% are normally considered to be ionic compounds. 

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