Dictionary > Covalent bond

Covalent bond

Definition

noun
plural: covalent bonds
A type of chemical bond wherein two or more atoms share one or more electron pairs

Details

Overview

A chemical bond holds atoms, ions, or molecules together in a chemical compound. Three types of chemical bonds that are deemed as biologically important are (1) ionic bonds, (2) covalent bonds, and (3) hydrogen bonds.

Covalent bond – characteristics

Covalent bond – characteristics

A covalent bond is known for the sharing of electrons between two atoms. Rather than the process of giving and receiving, covalent bonding entails the sharing of electrons in pair(s). The electrons travel between the nuclei of the atoms, being held together but kept at a stable distance apart. The prefix co– in its name specifies togetherness, equality, or jointly. Thus, covalent apparently indicates being jointly or togetherness in valence.

Covalent bond – characteristics

An electron pair (also called bonding pair or Lewis pair) consists of two electrons in the same molecular orbital but have opposite spins. In covalent bonding, the electrons are neither lost nor gained but are shared in pair. For instance, the carbon atom has four valence electrons in its outer shell. Rather than lose them, it tends to share them with another atom.

Covalent bond – characteristics

Electronegativity refers to the ability of an atom to attract electrons towards it. In a covalent bond, the electronegativities of the two atoms are neither strong nor weak but somewhat similar, thus, they tend to share electrons. The two atoms need not be the same elements but they need to have comparable electronegativities for covalent bonding to occur.

Types of covalent bonds

There are different types of covalent interactions, e.g. sigma (σ) bond and pi (π) bond. σ bonds are formed by head-on overlapping between atomic orbitals. It is the strongest type of covalent bond. π bonds are covalent bonds formed when the two lobes of an orbital on one atom laterally overlap the two lobes of an orbital on another atom.
A covalent bond may be single, double, or triple. A single bond (-) is when the atoms share two electrons. It is usually a sigma (σ) bond. For example, a water molecule has two hydrogen atoms and a central oxygen atom that are held together by two single covalent bonds. Each hydrogen atom shares a pair of electrons with the oxygen atom.
A double bond (=) is the sharing of four electrons between two chemical elements. It is usually comprised of the stronger σ bond and the weaker pi (π) bond. Example of a double bond is that found in alkenes, azo compounds, imines, and sulfoxides.
When the covalent bond involves six electrons between two atoms, it is a triple bond. A triple bond (≡) usually has one σ bond and two π bonds. Example is that found in alkynes, cyanides, isocyanides, and carbon monoxide.
The single bond is the weakest of the three since there is only one bond that connects two atoms together.

Organic compounds

Covalent bonds, similar to other chemical bonds, help to form a chemical compound. A chemical compound is a substance comprised of more than one type of atoms. Thus, a substance that is made up of only one type of atom is not a compound but a chemical element. An organic compound, for instance, is a compound that generally contains carbon atoms that are covalently bound to other atoms.
Organic compounds are of vital importance because all living things are based on these compounds. Examples of organic compounds are carbohydrates, lipids, proteins and nucleic acids.

Covalent bond vs. Ionic bond

While ionic bond involves the transferring of electrons from one to another, a covalent bond involves the sharing of electrons between atoms in order to achieve the stable configuration. It is argued that there is no pure ionic bonding. An ionic bond has a covalent character in it. The bond is said to be ionic rather than covalent there is a large difference in electronegativity between the two atoms.
Here is a tabulated summary of the major differences between ionic bond and covalent bond:1

Ionic bond Covalent bond
formation Ionic bond is formed by the transfer of electrons between atoms of one metal and one non-metal. The compound that results in an ionic bond is called ionic compound. Covalent bond is formed by the sharing of electrons between atoms of two elements, such as between two non-metals.
electronegativity (i.e. the ability of an atom to attract electrons towards it) The strong electronegativity of one atom attracts electron(s) from another atom. The atom that is strongly electronegative can gain electron(s) and becomes an anion. Conversely, the atom that is weakly electronegative loses electron(s) and becomes a cation. electronegativity of one atom is not strong enough or is somewhat the same as that of another atom, thus, the atoms tend to share rather than get or give electrons to achieve a stable electron configuration
salt formation The electrostatic attraction between anion and cation forms an ionic compound. Many of the ionic compounds are referred to as salts since they can be formed by the neutralization reaction between a base (e.g. OH) and an acid (H+). The bond that forms between the atoms does not result in the formation of a salt.
state at room temperature solid, with a crystallographic lattice liquid or gaseous
polarity high low
types single bond, double bond, triple bond, (depending on sigma and pi bonds involved)

Covalent bond vs. Hydrogen bond

As the name implies, a hydrogen bond is a chemical bond wherein hydrogen serves as a bridge between two atoms. Similar to a covalent bond, the hydrogen bond is a common chemical bond in organic compounds, particularly nucleic acids and proteins. The hydrogen bond is responsible for the formation of secondary and tertiary structures of nucleic acids and proteins.
One of the major distinctions between a covalent bond and a hydrogen bond is the electronegativities of the atoms involved. In a covalent bond, the electronegativities of the two atoms are comparable. Conversely, hydrogen bond forms when the slightly positive hydrogen atom of a polar covalent bond forms an electrostatic link with the more electronegative atom of a polar covalent bond in the same or another molecule.

Supplementary

Synonym

  • molecular bond

Derived term

  • Coordinate covalent bond
  • Further reading

    Compare

    See also

  • chemical bond
  • chemical compound
  • Reference

    1. Covalent Bonds vs Ionic Bonds. (13 January 2017). Retrieved from ://chem.libretexts.org/Bookshelves/Physical-and-Theoretical-Chemistry-Textbook-Maps/Supplemental-Modules-(Physical-and-Theoretical-Chemistry)/Chemical-Bonding/Fundamentals-of-Chemical-Bonding/Covalent-Bonds-vs-Ionic-Bonds Link

    © Biology Online. Content provided and moderated by Biology Online Editors