Covalent bonding is basically when atoms share pairs of electrons in order to gain greater stability. It is regarded as a balance of attractive and repulsive forces and can result in the development of an outer shell by atoms within a molecule who share their outer electrons. Non-metal atoms are the most common form of atoms that do this and can form between one and three bonds with other atoms, resulting in an amount of stability necessary to maintain their structure with the greatest strength possible. The theory of this type of bonding dates back as far as the 12th century but was famously documented by Isaac Newton in his Query 31 as part of his work “Opticks.” Since that time the theory has evolved greatly and physicists from all over the world have researched the topic.
Covalent bonding is necessary in order to achieve what is known as a noble gas configuration, which requires that molecules have eight valence electrons. This can be achieved in various ways but is necessary in order to satisfy what is known as the Octet Rule, and their designation as a noble gas. One of the most prevalent theories regarding covalent bonding is called the Lewis Theory and was proposed by G.N. Lewis in 1916. This was basically a compilation of theories that were widely accepted at the time of publication and dealt primarily with the valence electrons of an atom. The Lewis Theory states that atoms share electrons equally, although in nature this cannot be the case for they can never be equal.
This sharing of electrons can result in what is called a polar compound, such as water, and requires that the orbitals of a molecule overlap and that the area in which they do so is occupied by a pair of electrons, called the mode of Orbital Overlap. These two electrons must have opposite spins and the greater the overlap, the stronger the outer shell that is formed. The Lewis Theory further depends upon the mathematical function of Molecular orbit, which is used to decipher the behavior of an electron. This mathematical function is used to calculate the properties of an electron within a specific region and is used to determine which regions the electrons have combined.
As the years progressed the theory of covalent bonding was expanded upon to include the theories of both covalent bonding and ionic bonding, both of which are important models of thought regarding the subject. Also evolving over the years were the theories of resonant bonding, hypervalent bonding, electron-deficient bonding and aromatic bonding, all of which contributed greatly to the understanding of how covalent bonds were formed.