Covalent bonding is a form of
chemical bonding that is characterized by the sharing of pairs of
electrons between
atoms, or between atoms and other covalent bonds. In short, attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding. Covalent bonding includes many kinds of interactions, including
σ-bonding,
π-bonding, metal-metal bonding,
agostic interactions, and
three-center two-electron bonds. The term covalent bond dates from 1939. The prefix co- means jointly, associated in action, partnered to a lesser degree, etc.; thus a "co-valent bond", essentially, means that the atoms share "
valence", such as is discussed in
valence bond theory. In the molecule H2, the hydrogen atoms share the two electrons via covalent bonding. Covalency is greatest between atoms of similar
electronegativities. Thus, covalent bonding does not necessarily require the two atoms be of the same elements, only that they be of comparable electronegativity. Because covalent bonding entails sharing of electrons, it is necessarily
delocalized. Furthermore, in contrast to electrostatic interactions ("
ionic bonds") the strength of covalent bond depends on the angular relation between atoms in polyatomic molecules.
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The combination of two or more atoms by sharing electrons so as to achieve chemical stability under the octet rule. Atoms that form covalent bonds generally have outer energy levels containing three, four, or five electrons. Covalent bonds are generally stronger than other bonds.