Definition of Covalent Bond
Covalent bond or covalent bonding means the union of atoms in the molecules like hydrogen, chlorine, oxygen, water, etc, and most of the hydrocarbon like methane, ethane, propane, etc. The covalent bond is formed by sharing a pair of electrons between the atoms in the molecules or compounds. In such a way the participating covalent bonded or bonding atoms complete its octets structure. It is easy to understand the formation of the ionic bond by the definition but much difficult to gain an understanding of the covalent bonds in science. Therefore, covalent bonds may be defined as the forced holding together atoms through the sharing of electrons in chemistry.
American scientist G. N Lewis first points out that, it was possible for forming the covalent bond in a molecule to attain an inert gas structure without any transference of electrons or ionic bonds. Therefore, Lewis theory clearly explains the formation of the covalent bonds through the sharing of electrons and most types of chemical properties of covalent bonding. But Lewis theory does not provide the mechanism of sharing of electrons leading to the stability of the covalent bonding. The mechanism of sharing of electrons given from quantum mechanics.
Example of Covalent Bonding Molecules
The hydrogen atom has an electronic configuration 1s1. When two such atoms combine to form diatomic hydrogen molecules. Hence the covalent bonds hold the atoms together to form a hydrogen molecule. In each hydrogen atom attain stable inert gas electronic configuration.
A chlorine atom has seven electrons in the outermost quantum energy level. According to Lewis, two chlorine atoms unite to form the covalent chlorine molecule. By covalent chemical bonding, each atom contributes electrons to make a pair to be shared by both atoms. Lewis representation extended to cover multiple covalent molecular bonds also. For example, molecular bond in oxygen, carbon dioxide, ethylene, acetylene molecules formed by multiple covalent bonding.
Lewis Covalent Bond Structure
Counting the outer quantum shell electrons or valence electrons of the combing atoms. If species are cation then substruct on the electron. But for anion add on electrons for each negative charge. Put the larger or less electronegative atom as the central atom.
Arrange the electrons pairs keeping in mind to allow for octet for the atoms. For the first period chemical elements in the periodic table like boron, carbon, nitrogen, oxygen, and fluorine forming the covalent bond by sharing one or more electrons. However, hydrogen has one electron in the valence shell. Therefore, hydrogen may not be suitable for the octet rule. Another example in learning chemistry, octet will work alright for the covalent bond in PCl3 but not for PCl5.