The number of chemical bonds that an element forms to complete its octet is called as covalency. For example; Nitrogen has 5 valence electrons and belongs in Group VA. Nitrogen requires three more electrons to complete its octet therefore it will form three chemical bonds to get three more electrons from other element. In other words we can say that total six electrons involve in three chemical bonds between two bonding atoms. These six electrons are called as bonding electrons.Bonding electrons
can be defined as the electrons which involve in the bond formation between two elements. Similarly Carbon has four valence electrons and requires four more electrons from other element to get the octet configuration. Therefore it will form four covalent bonds that involve total eight bonding electrons. Since all valance electrons involve in the bond formation therefore there is no non-bonding pair of electron with carbon atom.
Let’s take an example of sodium atom. It has one electron in 3s and requires 7 electrons to get the octet configuration or it can lose that valence electron. Instead of accepting 7 electrons it’s easier to lose one valence electron. Therefore sodium forms sodium ion with positive charge. So we can say that all atoms either lose or gain electrons to get the octet configuration.
They can also share their valence electrons with other atoms to complete their octet. It results the formation of covalent bond between two bonding atoms. The bonding electrons are valance electrons of bonding atoms which involve in the bond formation. The valence electrons which do not take part in the bond formation are called as non-bonding electrons.
For example; Oxygen (O) and fluorine (F)
require a couple of electrons to make a filled shell therefore they can share electrons to form a covalent bond. Another way is to borrow electrons and form an ionic or electrovalent bond. One sodium atom and one fluorine atom will involve in the formation of ionic bond by transfer of valence electron from sodium to fluorine atom. This transfer completes the octet of both the bonding atoms and provides stability to them.
So we can say that bonding electrons come from the valence shell of the bonding atoms. Chemical bonds can be covalent type or ionic type. It depends on the difference of electro negativities of the bonding atoms. If the different is more than bonding atoms involve in the formation of ionic bond whereas less difference tend to form covalent bond by equal sharing of bonding electrons from both bonding atoms.
Ionic and covalent bonds
are the two extremes of chemical bonding as ionic bond is formed by complete transfer of electrons whereas covalent bond is formed by equal sharing of electrons between bonding atoms. Bonding pair of electrons define as the pair of electrons between bonding atoms which involve in the formation of chemical bond.
Some of the covalent bonds are formed between atoms with enough difference of electro negativity of bonding atoms. The difference between electro negativity induces polarity in the covalent bond and such bonds are called as polar covalent bonds.
The polarity of a compound depends on the symmetry and on differences in electro negativity between bonding atoms. In such polar covalent bonds, the bonding electrons are shifted towards more electro negative bonding atom.
Carbon molecules are mainly involve in the formation of covalent bonds because carbon atom contains 4 electrons
in its valence shell and requires four more electrons to complete the octet configuration.
Therefore each carbon atom can form four covalent bonds with other or same element to get stability. Due to tetra-valency of carbon atoms, they can form long chain of compounds and this property of carbon atom is called as catenation. Let’s take an example of carbon bonding in carbon dioxide molecule.
Like other compounds, in CO2 molecule also, carbon atom forms four covalent bonds 2 with each oxygen atom. Four valence electrons of Carbon atom forms covalent bonds with two oxygen atoms by equal sharing of electrons between C and O. It completes the octet configuration of Carbon atom and stabilizes it. On the other hand, each oxygen atom has six valence electrons and can share their two electrons to get octet configuration. Remaining four electrons of each oxygen atom do not involve in the bonding and called as non-bonding electrons. Hence there are total four covalent bonds between C and O
with total eight bonding electrons.