Polar, Nonpolar, and Ionic Bonds

There is, of course, a strong correlation between AVEE and electronegativity. As shown for a few atoms in Table 2, multiplying AVEE values by 1.8 yields numbers very close to electronegativity values. For historical reasons, most chemists use electronegativity values to estimate the electron drawing power of atoms in molecules. 

Describe the trend in EN as one moves from left to right across a period of the periodic table. 

Compare the trends observed in CTQs 2 and 3 to the corresponding trends in ionization energy and explain any observed relationship. 

A nonpolar covalent bond formed between identical atoms. 

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I identify or predict polar, nonpolar, and ionic bonds by comparing electronegativities. 

Use electronegativity differences to identify nonpolar covalent, polar covalent, and ionic bonds. (Section 8.4)... 

Nonpolar covalent, polar covalent, and ionic bonding. 

Solubility of polar molecules The ability of a substance to dissolve in another substance is known as the physical property solubility. The bond type and the shape of the molecules present determine solubility. Polar molecules and ionic compounds usually are soluble in polar substances, but nonpolar molecules dissolve only in nonpolar substances. See Figure 9-19. Solubility will be covered in detail in Chapter 15. 

Figure 3.6 summarizes the general differences between nonpolar covalent bonds, polar covalent bonds, and ionic bonds. 

Polar bonds fall between the extremes of nonpolar covalent bonds and ionic bonds. In a covalent bond between two atoms of the same element, there is no charge separation that is, the negative charge of the electrons is evenly distributed over the bond. In ionic bonds there is complete separation of the charges, and in polar bonds the separation falls somewhere in between. 

FIGURE 5.7 Nonpolar, polar, and ionic bonds, (a) In a nonpolar molecule such as H, the valence electron density is equally shared by both atoms, (b) In a polar molecule like HF, the valence electron density is shifted toward the fluorine atom. An arrow is used to show the direction of molecular polarity, with the arrowhead pointing toward the negative end of the molecule and the plus sign at the positive end of the molecule, (c) In ionic compounds such as NaCI, the valence electron or electrons of the metal are transferred completely to the nonmetal to give ions. 

A significant difference should be noted between Pauling s treatment of valence bonds and the corresponding NRT description of polar covalent or ionic bonding. In Pauling s formulation each polar bond requires two distinct resonance structures for its depiction, one covalent and one ionic. However, in the NRT framework each localized 2-center electron pair is represented as a bond-line of a single resonance structure, whether the bond is polar (ca /cb) or nonpolar (ca = cb)- Avoidance of covalent-ionic resonance in the NRT framework greatly reduces the number of NRT resonance structures required in expansions such as equation (26). 

Most chemical bonds are neither totally covalent nor totally ionic. As the difference in electronegativities between the two atoms increases, chemical bonds change from nonpolar covalent to polar covalent and then to ionic as the polarity of the bond increases. 

The Lewis structure indicates that KrF2 is nonpolar. Thus, it only has very weak London dispersion forces between the molecules. SeF2 is polar and the molecules are attracted by dipole—dipole attractions, which are stronger than London. SnF2 has the highest melting point, because of the presence of strong ionic bonds. 

In nonionics the molecule has a nonpolar hydrophobic portion and a more polar, but not ionic, hydrophilic part capable of hydrogen bonding with water. For some years the major nonionics were the reaction products of ethylene oxide and nonylphenol and are called nonylphenol ethoxylates... 

Since all bonds in these compounds are covalent, these molecules do not have strong electric fields, and are therefore soluble in nonpolar and weakly polar solvents, like benzene. Ionic complexes, if... 

The ionic bond and the nonpolar covalent bond represent the two extremes of chemical bonding. The ionic bond involves a transfer of one or more electrons, and the nonpolar covalent bond involves the equitable sharing of electrons. The character of a polar covalent bond falls between these two extremes. 

In this chapter, we explored two types of chemical bonds ionic and covalent. Ionic bonds are formed when one or more electrons move from one atom to another. In this way, the atoms become ions—one positive, the other negative—and are held together by the resulting electrical attraction. Covalent bonds form when atoms share electrons. When the sharing is completely equitable, the bond is nonpolar covalent. When one atom pulls more strongly on the electrons because of its greater electronegativity, the bond is polar covalent and a dipole may be formed. 

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