The attraction between molecules, atoms, or ions is referred to as a chemical bond. Chemical bonds lead to the formation of a chemical compound which is mainly composed of many identical molecules. The attraction between atoms is as a result of the behavior of valence electrons of an atom. The strength of these bonds varies and can either be strong or weak. Strong bonds, also known as primary bonds, are formed by the sharing or transfer of electrons. There are three main types of strong chemical bonds; ionic bonds, covalent bonds, and metallic bonds. This article focuses on the covalent bond.
A covalent bond is also known as a molecular bond and can be described as a type of chemical bonding that involves an electron pair between at least two atoms. These pairs of electrons are also known as bonding pairs or sharing pairs. The sharing of the bonding pairs of electrons allows the atoms to attain a stable outer electron shell. A covalent bond is mainly formed between atoms of nonmetals with relatively close or identical electronegativity values. The term “covalent bond” was introduced in 1939, though the term “covalence” had been in use much earlier.
Types of Covalent Bonds
There are different types of covalent bonds which are a result of the atomic orbitals having specific directional properties. Covalent bonds are broadly divided into two types; pure (nonpolar) covalent bonds and polar covalent bonds. Pure bonds result from the equal sharing of electron pairs by the atoms. Since only with the same electronegativity values are involved in the sharing of electron pairs, nonpolar bonds include an atom with an electronegativity difference of below 0.4. Examples of nonpolar bonds are H2 and N2. A polar covalent bond is created by atoms with unequal electronegativity values. The electronegativity difference of a polar covalent bond is from 0.4 to 1.7.
The strongest covalent bond is the sigma () bond created by the head-on overlap of orbitals of two different atoms while the Pi () bonds are the weakest, created by the lateral overlapping between orbitals. An example of a sigma bond is the single covalent bond in which an electron pair shared by two atoms. The double bond which involves the two atoms sharing of two pairs of electrons instead of the usual one pair consists of a sigma bond and a Pi bond. Triple bond involves the sharing of three pairs of electrons by two atoms, consists of one sigma bond and two Pi bonds. Other covalent bonds are 3-center 2-electron bond, 3-center 4-electron bond, and one-and three-electron bond.
Example of a Covalent Bond
A covalent bond exists between each hydrogen and the oxygen in water molecules (H2O). Each covalent bond contains one electron from the oxygen atom and one electron from the hydrogen atom. A hydrogen molecule is made up of two hydrogen atoms that are joined together by a covalent bond, hence H2. Each of the hydrogen atoms requires an electron pair for the outer electron shell to be stable. The molecule is held together by the atomic molecule.
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