Covalency is the sharing of electrons between the atoms of non-metals. A covalent bond is formed when two atoms of non-metal contribute electron(s) equivalent to their valency for sharing.
After the bonding, both atoms will attain a stable octet or duplet structure of rare gases. Electrons are not transferred because the atoms involved are electron acceptors. The pair of electrons shared is known as the shared pair of electrons.
Diatomic molecules are formed by covalent bonding. e.g Cl2, H2, N2, O2. In Chlorine molecules, only one electron is used in forming a covalent bond. The other six electrons form three lone pairs of electrons.
Formation of Chlorine molecule (Cl2)
Formation of Hydrogen molecule (H2)
Formation of Oxygen molecule(O2)
Formation of Nitrogen Molecule (N2)
Formation of Water Molecule (H2O)
A water molecule contains 2 lone pairs of electrons and two shared pairs of electrons. The water molecule is a V-shape.
The mode of formation of H2S is similar to that of H2O.
Formation of Ammonia (NH3)
Ammonia molecule contains 1-Lone pair of electrons and 3-shared pair of electrons.
Ammonia molecule is pyramidal-shaped. The mode of formation of PH3, PCl3, and NCl3 is similar to that of HN3.
Formation of Methane (CH4)
Methane molecule (CH4) contains 4 shared pairs of electrons. CH4 molecule is tetrahedral in shape. The mode of formation and the shape of CCl4 are similar to that of CH4.
Formation of Carbon (IV) Oxide (CO2)
Carbon (IV) oxide molecule – CO2
CO2 is Linear shape O = C = O
Types of Covalent bond
1. Non-polar covalent bond.
2. Polar covalent bond.
Non-Polar Covalent bond:
Non-polar covalent bonds are covalent bonds formed between two non-metals of the same or about the same electronegativity. In non-polar molecules, electron pair is shared equally i.e there is a uniform distribution of electron density around the nuclei. e.g N2, H2, Cl2 ,Br2
Polar Covalent bond:
Polar covalent bonds are covalent bonds formed between two non-metals having different electronegativity. The electron pair is not shared equally i.e non-symmetrical. The atoms carry partial separation of charges called permanent dipole e.g H2O, HCl, H2S, HF
Factors that Determine Covalent Bonds:
2. Electron affinity.
3. Ionization Energy.
Characteristic Properties of Covalent Compounds:
1. They have low melting and boiling point.
2. They are non-electrolytes or they do not conduct electricity.
3. They are not soluble in water or polar solvents, but soluble in non-polar solvents like Benzene, ether, etc.
4. They are gases or volatile liquids.
5. They consist of molecules.