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The correlation between Mulliken electronegativities (x-axis, in kJ/mol) and Pauling electronegativities (y-axis).Robert S. Mulliken proposed that the arithmetic mean of the first ionization energy (E i) and the electron affinity (E ea) should be a measure of the tendency of an atom to attract electrons: [9] [10] = +
Electron capture for almost all non-noble gas atoms involves the release of energy [4] and thus is exothermic. The positive values that are listed in tables of E ea are amounts or magnitudes. It is the word "released" within the definition "energy released" that supplies the negative sign to ΔE.
This means that the two shared electrons are closer to one of the atoms than the other, creating an imbalance of charge. Such bonds occur between two atoms with moderately different electronegativities and give rise to dipole–dipole interactions. The electronegativity difference between the two atoms in these bonds is 0.3 to 1.7.
Ionic bonds generally occur when the difference in electronegativity between the two atoms is greater than 2.0; Pauling based this classification scheme on the partial ionic character of a bond, which is an approximate function of the difference in electronegativity between the two bonded atoms. He estimated that a difference of 1.7 corresponds ...
Using the various properties of molecules, such as the energy required to break bonds and the dipole moments of molecules, he established a scale and an associated numerical value for most of the elements — the Pauling Electronegativity Scale — which is useful in predicting the nature of bonds between atoms in molecules. [44]
Electronegativity is not a uniquely defined property and may depend on the definition. The suggested values are all taken from WebElements as a consistent set. Many of the highly radioactive elements have values that must be predictions or extrapolations, but are unfortunately not marked as such.
Oxidation and reduction always occur in a paired fashion such that one species is oxidized when another is reduced. For cases where electrons are shared (covalent bonds) between atoms with large differences in electronegativity, the electron is assigned to the atom with the largest electronegativity in determining the oxidation state.
Covalent and ionic bonding form a continuum, with ionic character increasing with increasing difference in the electronegativity of the participating atoms. Covalent bonding corresponds to sharing of a pair of electrons between two atoms of essentially equal electronegativity (for example, C–C and C–H bonds in aliphatic hydrocarbons).