A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, and other covalent bonds. In short, the attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding.
The concept of Covalent bond was introduced by G.N.Lewis in 1961. The compounds formed by covalent bond are known as covalent compounds.
For Example: In the molecule H2, the hydrogen atoms share the two electrons by covalent bonding when they approach each other. Then each hydrogen atom acquire the electronic configuration of the noble gas Helium, 1s2.
The bonding atoms involved may share more than one pair of electrons which depends on their requirement of completing the octet.
For every pair of electrons shared between two atoms, a single covalent bond is formed. Some atoms can share multiple pairs of electrons, forming multiple covalent bonds. For example, oxygen (which has six valence electrons) needs two electrons to complete its valence shell. When two oxygen atoms form the compound O2, they share two pairs of electrons, forming two covalent bonds.
Bond Length or bond distance is the average distance between nuclei of two bonded atoms in a molecule.
The number of electrons, which an atom contributes towards mutual sharing during the formation of a chemical bond is called its covalency in that compound. Thus, the covalency of hydrogen in H2 (H – H, H: H)
Comparison between single, double and triple bond
Single, double and triple covalent bonds differ from each other in the following ways.
• Single bond is formed by the sharing of one electron pair i.e. two electrons are involved where as a double bond is formed by the sharing of two electron pairs i.e. four electrons are involved, whereas a triple bond involves sharing of three electron pairs i.e. six electrons are used in triple bond formation.
• The bond lengths follow the order:
Triple bond length < Double bond length < Single bond length
Greater the attraction between the nuclei and the electrons smaller will be the distance between them. Hence it is more difficult to separate the triple bond as compared to double and single bond. This means more energy is required to separate triple bond as compared to double and single bond. Hence the bond energy will be in the following sequence:
Triple bond > Double bond > Single bond.