Electronegativity The relative ability

We have seen that when a metal and a nonmetal react, one or more electrons are transferred from the metal to the nonmetal to give ionic bonding. On the other hand, two identical atoms react to form a covalent bond in which electrons are shared equally. When different nonmetals react, a bond forms in which electrons are shared unequally, giving a polar covalent bond. The unequal sharing of electrons between two atoms is described by a property called electronegativity the relative ability of an atom in a molecule to attract shared electrons to itself... 

Electronegativity the relative ability of an atom to attract shared electrons... 

The electronegativity of an element indicates the relative ability of its atoms to attract electrons to form chemical bonds. According to the graph, as yon move across a period in the periodic table —... 

In HO -catalyzed hydrolysis (specific base catalyzed hydrolysis), the tetrahedral intermediate is formed by the addition of a nucleophilic HO ion (Fig. 3.1, Pathway b). This reaction is irreversible for both esters and amides, since the carboxylate ion formed is deprotonated in basic solution and, hence, is not receptive to attack by the nucleophilic alcohol, phenol, or amine. The reactivity of the carboxylic acid derivative toward a particular nucleophile depends on a) the relative electron-donating or -withdrawing power of the substituents on the carbonyl group, and b) the relative ability of the -OR or -NR R" moiety to act as a leaving group. Thus, electronegative substituents accelerate hydrolysis, and esters are more readily hydrolyzed than amides. 

The relative abilities of two bonded atoms to attract and bind electron density within their basins are a measure of their relative electronegativities. It is found, for example, that H is slightly more electronegative than C in saturated hydrocarbons and that the electronegativity of C relative to H increases with the degree of unsaturation and with the extent of geometric strain. 

Electron affinity is a measure of the tendency of an atom to accept an electron. Excluding noble gases, electron affinity increases as the atomic number increases within a given period and decreases with an increase in atomic number within a group. The scale of electronegativities allows a chemist to evaluate the electron affinity of specific atoms when they are incorporated into a compound. Recall from Chapter 6 that electronegativity indicates the relative ability of an atom to attract electrons in a chemical bond. 

Laboratory measurements show that most real bonds are neither fully ionic nor fully covalent, but instead possess a mixture of ionic and covalent character. Bonds in which there is a partial transfer of charge are called polar covalent. This section provides an approximate description of the polar covalent bond based on the relative abilities of each atom to attract the electron pair toward its nucleus. This ability is estimated by comparing the electronegativity values for the two atoms. 

Electronegativity is dehned as the relative ability of an atom in a molecide to attract the electrons shared in a bond. The difference in electronegativity values between the atoms involved in a bond determines the polarity of that bond. 

Electronegativity represents the relative ability of an atom in a molecule to attract shared electrons to itself. The larger the difference in electronegativity between two atoms joined in a bond, the more polar is the bond. Examples depend on student choice of elements. 

Electronegativity and Polarity Electronegativity refers to the relative ability of elements to attract electrons within a chemical bond. Electronegativity increases as you move to the right across a period in the periodic table and decreases as you move down a column. When two nonmetal atoms of different electronegativities form a covalent bond, the electrons in the bond are not evenly shared and the bond is polar. In diatomic molecules, a polar bond results in a polar molecule. In molecules with more than two atoms, polar bonds may cancel, forming a nonpolar molecule, or they may sum, forming a polar molecule. 

As this description suggests, the extent of aromaticity in these systens depends on the relative ability of the heteroatom to donate its lone electron pair, in turn desoibed by its respective electronegativity (Table 1-2). Consequaitly, the aromalic character increases along the series fiiran < pyrrole < thiophene, a trend that is reflected in relative reactivity and stabihty. 

Electronegativity When atoms combine chemically with each other, they do so by forming a chemical bond. This bond involves either the transfer of electrons or sharing of electrons to varying degrees. The nature of the bond between two atoms depends on the relative ability of each atom to attract electrons from the other, a property known as electronegativity. 

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