Covalent bonding is a description of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. In short, attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding. The term "covalence", in regards to bonding, was first used in 1919 by Irving Langmuir in a Journal of American Chemical Society article entitled "Isomorphism, Isosterism, and Covalence" wherein he states:^[1] A chemical bond is the PHYSICAL process responsible for the ATTRACTIVE INTERACTIONS between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... e- redirects here. ... “Atomic” redirects here. ... Irving Langmuir at home (c. ... In mathematics, an isomorphism (in Greek isos = equal and morphe = shape) is a kind of mapping between objects, devised by Eilhard Mitscherlich, which shows a relation between two properties or operations. ... The phenomenon of substances having molecules with the same number of atoms and the same total number of electrons is known as isosterism. ...

The term covalent bond is from 1939.^[2] The prefix co-, such as in co-partner, 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. If an atom, for example, had a +1 valence, meaning it was missing an electron (with respect to the octet rule), and another a -1 valence, meaning it had an extra electron (with respect to the octet rule), then a bond between these two atoms would result because they would be complementing or sharing their out of balance valence tendencies. In general, bonds are defined by a mutual attraction that holds the resultant molecule together. Often, bonding occurs in such a way that the outer electron shells of the participating atoms become filled. In contrast to electrostatic interactions labeled as "ionic bonds," the strength of covalent bond depends on the angular relation between atoms in polyatomic molecules. Covalent bonding is most important between atoms with similar electronegativities. Covalent bonding is often delocalized. Covalent bonding is a broad concept and includes many kinds of interactions, including σ-bonding, π-bonding, metal-metal bonding, agostic interactions, and three-center two-electron bonds.^[3][4] The valence bond theory is a concept in chemistry that explains the nature of a chemical bond in a molecule [1] . It has its origins with G.N. Lewis who in 1916 first proposed that a chemical bond forms by the interaction of two shared bonding electrons, with the representation... In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. ... The bonding in carbon dioxide The octet rule is a simple chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, similar to the electronic configuration of a noble gas. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Example of a sodium electron shell model An electron shell, also known as a main energy level, is a group of atomic orbitals with the same value of the principal quantum number n. ... Electron configurations of lithium and fluorine. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond. ... Agostic complexes are coordination compounds where the σ bond of a ligand serves as the electron pair donor. ... A three-center two-electron bond is an electron deficient chemical bond where three atoms share two electrons. ...

Schemes depicting covalent (left) and polar covalent (right) bonding in a diatomic molecule. The arrows represent electrons provided by the participating atoms.

Image File history File links Download high-resolution version (1692x898, 27 KB) I, Smokefoot, drew and release this. ... Image File history File links Download high-resolution version (1692x898, 27 KB) I, Smokefoot, drew and release this. ...

History

The idea of covalent bonding can be traced to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs between atoms. He introduced the so called Lewis notation or electron dot notation or The 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, in which bond-forming electron pairs are represented as solid lines, is shown alongside. Lewis in the Berkeley Lab Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous American physical chemist. ... G. N. Lewis Lewis structures, also called electron-dot structures or electron-dot diagrams, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. ...

Early concepts in covalent bonding arose from this kind of image of the molecule of methane. Covalent bonding is implied in the Lewis structure that indicates sharing of electrons between atoms.

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. Image File history File links Covalent. ... Image File history File links Covalent. ... Methane is the principal component of natural gas. ... G. N. Lewis Lewis structures, also called electron-dot structures or electron-dot diagrams, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. ... Fig. ... Walter Heinrich Heitler (02. ... Fritz Wolfgang London (March 7, 1900–March 30, 1954) was a German-born American physicist for whom the London force is named. ... Molecular hydrogen, H2, is a molecule formed from two atoms of hydrogen. ... An atomic orbital is the description of the behavior of an electron in an atom according to quantum mechanics. ...

Bond polarity

A "pure" covalent bond occurs between atoms with identical electronegativity, although some texts suggest that the term should be used when the difference is less than 0.2. According to a widely-accepted definition, polar covalence describes bonds between atoms whose electronegativities differ by less than 2.1 but greater than 0.5. Polar covalency also describes the so-called a coordinate covalent bond, also known as a dative covalent bond, which occurs when one atom "gives" both of the electrons in the bond. The classic example is borane-ammonia. Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... It has been suggested that this article or section be merged with Covalent bond. ... Ammonia borane is the chemical compound with the formula H3NBH3. ...

Bond order

Bond order is a number that indicates the number of pairs of electrons shared between atoms forming a covalent bond. The term is only applicable to diatomic molecules, but is used to describe bonds within polyatomic compounds as well. Bond order is the number of bonds between a pair of atoms. ...

1. The most common type of covalent bond is the single bond, the sharing only one pair of electrons between two atoms. It usually consists of one sigma bond. All bonds with more than one shared pair are called multiple bonds.
2. Sharing two pairs is called a double bond. An example is in ethylene (between the carbon atoms). It usually consists of one sigma bond and one pi bond.
3. Sharing three pairs is called a triple bond. An example is in hydrogen cyanide (between C and N). It usually consists of one sigma bond and two pi-bonds.
4. Quadruple bonds are found in the transition metals. Molybdenum and rhenium are the elements most commonly observed with this bonding configuration. An example of a quadruple bond is also found in Di-tungsten tetra(hpp).
5. Quintuple bonds have been found to exist in certain dichromium compounds.
6. The only known molecules with true sextuple bonds (order 6) are diatomic Mo₂ and W₂, in the gaseous phase at very low temperatures. Although diatomic Cr₂ and U₂ have formal structures with twelve-electron bonds, their effective bond orders (derived from quantum chemistry calculations) are less than 5. There is strong evidence to believe that no two elements in the periodic table can form a bond with greater order than 6.^[5]

Most bonding of course, is not localized, so the following classification, while powerful and pervasive, is of limited validity. Three center bond do not conform readily to the above conventions. Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ bonds) are a type of covalent chemical bond. ... Ethylene (or IUPAC name ethene) is the chemical compound with the formula CH2CH2. ... Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ bonds) are a type of covalent chemical bond. ... Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (π bonds) are bonds with a single nodal plane containing the line segment between the two atoms. ... Hydrogen cyanide is a chemical compound with chemical formula HCN. A solution of hydrogen cyanide in water is called hydrocyanic acid or Prussic acid. ... Covalently bonded hydrogen and carbon in a molecule of methane. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ... General Name, Symbol, Number rhenium, Re, 75 Chemical series transition metals Group, Period, Block 7, 6, d Appearance grayish white Atomic mass 186. ... the hpp ligand anion Di-tungsten tetra(hpp) or W2(hpp)4 is a di-tungsten paddlewheel compound with four hpp or hexahydropyrimidopyrimidine ligands. ... A Quintuple Bond in chemistry is an unusual type of chemical bond first observed in 2005 in a chromium dimer in an organometallic compound. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... Quantum chemistry is a branch of theoretical chemistry, which applies quantum mechanics and quantum field theory to address issues and problems in chemistry. ... In chemistry, a three-center bond is a type of covalent bond, in which one pair of electrons joins three atoms rather than the usual two. ...

Resonance

Many bonding situations can be described with more than one valid Lewis Dot Structure (for example, ozone, O₃). In an LDS diagram of O₃, the center atom will have a single bond with one atom and a double bond with the other. The LDS diagram cannot tell us which atom has the double bond; the first and second adjoining atoms have equal chances of having the double bond. These two possible structures are called resonance structures. In reality, the structure of ozone is a resonance hybrid between its two possible resonance structures. Instead of having one double bond and one single bond, there are actually two 1.5 bonds with approximately three electrons in each at all times. For other uses, see Ozone (disambiguation). ... Resonance structures are diagrammatic tools in organic chemistry to symbolize resonant bonds between atoms in molecules. ...

A special resonance case is exhibited in aromatic rings of atoms (for example, benzene). Aromatic rings are composed of atoms arranged in a circle (held together by covalent bonds) that may alternate between single and double bonds according to their LDS. In actuality, the electrons tend to be disambiguously and evenly spaced within the ring. Electron sharing in aromatic structures is often represented with a ring inside the circle of atoms. In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ... Benzene, also known as benzol, is an organic chemical compound with the formula C6H6. ...

Current theory

Today the valence bond model has been supplanted by the molecular orbital model. In this model, as atoms are brought together, the atomic orbitals interact to form molecular orbitals, which are linear sums and differences of the atomic orbitals. These molecular orbitals are a cross between the original atomic orbitals and generally extend between the two bonding atoms. In chemistry, a molecular orbital is a region in which an electron may be found in a molecule. ...

Using quantum mechanics it is possible to calculate the electronic structure, energy levels, bond angles, bond distances, dipole moments, and electromagnetic spectra of simple molecules with a high degree of accuracy. Bond distances and angles can be calculated as accurately as they can be measured (distances to a few pm and bond angles to a few degrees). For small molecules, calculations are sufficiently accurate to be useful for determining thermodynamic heats of formation and kinetic activation energy barriers.

References

1. ^ Langmuir, I. (1919). "Isomorphism, Isosterism and Covalence." J. Am. Chem. Soc.; 1919; 41(10); 1543-1559.
2. ^ Merriam-Webster - Collegiate Dictionary (2000).
3. ^ March, J. “Advanced Organic Chemistry” $th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
4. ^ G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
5. ^ Roos, Björn O.; Antonio C. Borin, and Laura Gagliardi (January 2007). "Reaching the Maximum Multiplicity of the Covalent Chemical Bond". Angewandte Chemie International Edition. DOI:10.1002/anie.200603600. 

• http://www.chemguide.co.uk/atoms/bonding/covalent.html
• http://www.chem.ox.ac.uk/vrchemistry/electronsandbonds/intro1.htm
• http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html#c5

Merriam-Webster, originally known as the G. & C. Merriam Company of Springfield, Massachusetts, is a United States company that publishes reference books, especially dictionaries that are descendants of Noah Websters An American Dictionary of the English Language (1828). ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

• Covalent Bonds and Molecular Structure
• Bonding tutorials

This page aims to list well-known organic compounds, including organometallic compounds, to stimulate the creation of Wikipedia articles. ...

See also

• Chemical bond
• Ionic bond
• Linear combination of atomic orbitals
• Metallic bonding
• Hybridisation
• Hydrogen bond
• Noncovalent bonding
• Disulfide bond