Electronegative substances

Highly electronegative substances that can withdraw electrons partially and/or a substituent that removes electrons by resonance... 

Photoreductiom in Aqueous Solution. Solvated electrons form on the irradiation of natural water samples or of aqueous solutions of natural organic matter isolated from surface waters (12, 45, 46). The solvated electron is a powerful reductant that reacts rapidly with electronegative substances such as chlorinated, brominated, and iodinated compounds. The interaction of pho-toejected electrons and a halocarbon is demonstrated by the laser flash photolysis data shown in Figure 3. 

Electronegative substances attract electrons from the carbon atoms they are attached to, this further polarizes the O — H bond making ionization of the acid easier. 

The Swedish chemist Jons Jacob Berzelius took Davy s idea a step further. He postulated that matter consisted of combinations of electropositive and electronegative substances, classifying the parts by the pole at which they accumulated during electrolysis. 

Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with most organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. 

The bond dipoles m Table 1 3 depend on the difference m electronegativity of the bonded atoms and on the bond distance The polarity of a C—H 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—H bond and a C—O bond and that is the direction of the dipole moment In a C—H bond the electrons are drawn away from H toward C In a C—O bond electrons are drawn from C toward O As we 11 see m later chap ters the kinds of reactions that a substance undergoes can often be related to the size and direction of key bond dipoles... 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

This description would assign to the caesium atom in the caesium fluoride crystal a resultant charge + and to the fluorine atom a charge — It has seemed to me likely that in general all of the atoms in the complexes that constitute stable chemical substances have resultant electrical charges smaller than those shown by these most electropositive and electronegative atoms in their compounds with one another, and I have accordingly formulated the postulate of the essential electrical neutrality of atoms namely, that the electronic structure of substances is... 

Electronegativity differences (A x) between bonded atoms provide a measure of where any particular bond lies on the continuum of bond polarities. Three fluorine-containing substances, F2, HF, and CsF, represent the range of variation. At one end of the continuum, the bonding electrons in F2 are shared equally between the two fluorine atoms (A = 4.0 - 4.0 = 0). At the other limit, CsF (A = 4.0 - 0.7 = 3.3) is an ionic compound in which electrons have been fully transferred to give Cs cations and F" anions. Most bonds,... 

Acetone and CH3F contain electronegative atoms with nonbonding pairs, but neither has any highly polar H—X bonds. Thus, there is no hydrogen bonding between molecules of these substances. 

Most substances contain covalent bonds rather than ions. Nevertheless, the electrons in a bond between atoms of two different elements, such as FeO or CO, are polarized toward the more electronegative atom (see Figure 19-3 for electronegativities). For oxidation number purposes, we imagine that these electrons are transferred completely to the more electronegative atom. 

The bonding electrons in CO and CO2 are polarized in the direction of the O atoms, as shown by the electronegativities of C (2.5) and O (3.5). Thus, if these substances were ionic, CO would consist of C cations and O anions, and CO2 would contain cations and O anions. Accordingly, we assign O an oxidation number of-2 in both these compounds, whereas C has an oxidation number of +2 in CO and +4 in CO2. ... 

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