Attracting electrons Electronegativities

Linus Pauling, one of America s most famous chemists, devised a scale of numerical values reflecting the tendency of an atom to attract electrons. Electronegativity is a measure of the abiiity of an atom in a chemicai compound to attract eiectrons from another atom in the compound. The most electronegative element, fluorine, is arbitrarily assigned an electronegativity of four. Other values are then calculated in relation to this value. 

Electron Delocalization in the Conjugate Base With a of —1 4 nitnc acid is almost completely ionized m water If we look at the Lewis structure of nitric acid m light of what we have said about inductive effects we can see why The N atom m nitric acid IS not only electronegative m its own right but bears a formal charge of +1 which enhances its ability to attract electrons away from the —OH group... 

Another fundamental property of chemical bonds is polarity. In general, it is to be expected that the distribution of the pair of electrons in a covalent bond will favor one of the two atoms. The tendency of an atom to attract electrons is called electronegativity. There are a number of different approaches to assigning electronegativity, and most are numerically scaled to a definition originally proposed by Pauling. Part A of Table 1.6... 

A covalent bond will exhibit polarity when it is formed from atoms that differ in electronegativity, i.e., the ability to attract electrons. The order of electronegativity of some elements [50, p. 16] is... 

The two elements have similar electronegativity. (Note electronegativity is the power of an element to attract electrons to itself when present in a molecule or in an aggregate of unlike atoms it is a different property from the electrode potential, which depends on the free energy difference between an element in its standard state and a compound or ion in solution (see Section 20.1).) In addition a metal of a lower valency tends to dissolve a metal of a higher valency more readily than vice versa. 

Electronegativity (Section 2.1) The ability of an atom to attract electrons in a covalent bond. Electronegativity increases across the periodic table from right to left and from bottom to top. 

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 —... 

These definitions are clear, but they do not apply to the vast majority of real molecules in which the bonds are neither purely ionic nor purely covalent. Lewis recognized that a pair of electrons is generally not shared equally between two electrons because the atoms generally have different powers of attracting electrons, that is, they have different electronegativities, giving charges to both atoms. Such bonds are considered to have some covalent character and some ionic character and are known as polar bonds. 

Electronegativity measures the ability of an atom to attract electrons. 

Electronegativity (EN) is the ability of an element to attract electrons that it is sharing in a covalent bond. 

Atoms do not all have the same ability to attract electrons. When two different types of atoms form a covalent bond by sharing a pair of electrons, the shared pair of electrons will spend more time in the vicinity of the atom that has the greater ability to attract them. In other words, the electron pair is shared, but it is not shared equally. The ability of an atom in a molecule to attract electrons to it is expressed as the electronegativity of the atom. Earlier, for a homonuclear diatomic molecule we wrote the combination of two atomic wave functions as... 

As has just been described, when a covalent bond forms between two atoms, there is no reason to assume that the pair of electrons is shared equally between the atoms. What is needed is some sort of way to provide a relative index of the ability of an atom to attract electrons. Linus Pauling developed an approach to this problem by describing a property now known as the electronegativity of an atom. This property gives a measure of the tendency of an atom in a molecule to attract electrons. Pauling devised a way to give numerical values to describe this property that makes use of the fact that the covalent bonds between atoms of different electronegativity are more stable than if they were purely... 

Pauling based electronegativity values on bond energies between atoms, but that is not the only way to approach the problem of the ability of atoms in a molecule to attract electrons. For example, the ease of removing an electron from an atom, the ionization potential, is related to its ability to attract electrons to itself. The electron affinity also gives a measure of the ability of an atom to hold on to an electron that it has gained. These atomic properties should therefore be related to the ability of an atom in a molecule to attract electrons. Therefore, it is natural to make use of these properties in an equation... 

Electronegativity is defined as the tendency of an atom to attract electrons to itself in a chemical bond. 

Like thiazole, oxazole is a jt-electron-excessive heterocycle. The electronegativity of the N-atom attracts electrons so that C(2) is partially electropositive and therefore susceptible to nucleophilic attack. However, electrophilic substitution of oxazoles takes place at the electron-rich position C(5) preferentially. More relevant to palladium chemistry, 2-halooxazoles or 2-halobenzoxazoles are prone to oxidative addition to Pd(0). Even 2-chlorooxazole and 2-chlorobenzoxazole are viable substrates for Pd-catalyzed reactions. 

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