Electronegativity measures an atom’s ability to attract electrons. Differences in electronegativity predict bond strength. Covalent bonds share electrons, while ionic bonds strip electrons. The Pauling scale measures bond strength and predicts bond type.
Electronegativity is the degree to which an atom can attract bonding electrons to itself. The components of this relative measure are the ability of an atom to acquire and retain electrons. The differences between the electronegativities of two atoms can be used to predict the relative bond strength. Several scales have been proposed to express electronegativity.
Chemical bonds are the attractive forces between atoms that create molecules. Molecules are the building blocks of all matter. The nature of the chemical bonds determines many of the molecular properties.
Electrons travel in shells around atomic nuclei. Atoms are most stable when their electron shells are full or half-filled. Covalent bonds occur when one or more electrons are shared between atoms. The electron orbits closest to the more electronegative atom. Although the electron is shared in covalent bonds, the whole molecular structure is stronger.
In ionic bonds, the electronegative difference between two or more atoms is so great that the electron is stripped from the less electronegative atom. These bonds are polar, like tiny magnets. They can dissociate in water or other solvents into two or more separate ions.
In 1934, American scientist Robert S. Muliken suggested measuring electronegativity as half the difference between ionization energy (IE) and electron affinity (EA). IE is the energy required to remove an electron from an atom and EA is the energy released when an atom acquires an electron. His scale was not adopted because electron affinity was difficult to measure at the time.
Another American scientist, Linus Pauling, had developed an earlier scale based on the relative strength of chemical bonds. Fluorine, the most electronegative atom, has been assigned an electronegativity of 4.0. Lithium, on the opposite side of the periodic table, has been assigned a value of 1.0. Cesium, with a value of 0.7, is inferior to lithium. In general, electronegativity increases from left to right across the periodic table. Decreases from top to bottom.
The Pauling scale provides a good measure of the type of bond atoms will form. The electronegative difference between two nonmetallic atoms is small; hence, covalent bonds are formed. The carbon-nitrogen (CN bond) in pyridine (C5H5N) is an example. Carbon has an electronegativity of 2.5; nitrogen is 3.0; and the difference is 0.5.
A nonmetal and a metal atom form an ionic bond due to the large electronegative difference. Potassium chloride is an example (KCl). Potassium has a value of 0.8; chloride has a value of 3.0; and the difference is 2.2.
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