Covalent+bond

A covalent bond is a bond in which one or more pairs of electrons are shared by two atoms.

Atoms can combine to achieve an octet of valence electrons by sharing electrons. Two fluorine atoms, for example, can form a stable F2 molecule in which each atom has an octet of valence electrons by sharing a pair of electron .

A pair of oxygen atoms can form an O2 molecule in which each atom has a total of eight valence electrons by sharing two pairs of electrons. The term **covalent bond** is used to describe the bonds in compounds that result from the sharing of one or more pairs of electrons.

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons known as covalent bonding. Covalent bonding includes many kinds of interaction, including __ [|σ-bonding] __, [|π-bonding], metal-to-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" in essence, means that the atoms share "valence."

**History**
The term "covalence" in regard to bonding was first used in 1919 byIrving Langmuir in a //Journal of the American Chemical Society//article entitled "The Arrangement of Electrons in Atoms and Molecules". Langmuir wrote that "we shall denote by the term**covalence** the number of pairs of electrons which a given atom shares with its neighbors." The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs between atoms. He introduced the //Lewis notation// or//electron dot notation// or //Lewis dot structure// in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as double and triple bonds. Some examples of Electron Dot Notation are shown in the following figure. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines. While the idea of shared electron pairs provides an effective qualitative picture of covalent bonding,quantum mechanics is needed to understand the nature of these bonds and predict the structures and properties of simple molecules. Walter Heitler and Fritz London are credited with the first successful quantum mechanical explanation of a chemical bond, specifically that of molecular hydrogen, in 1927. Their work was based on the valence bond model, which assumes that a chemical bond is formed when there is good overlap between the atomic orbitals of participating atoms. These atomic orbitals are known to have specific angular relationships between each other, and thus the valence bond model can successfully predict the bond angles observed in simple molecules.