TRIPLE COVALENT BOND: A covalent bond formed by the mutual sharing of three pair of electrons is called a triple covalent bond, or simply a triple bond. A triple covalent bond is represented by three small horizontal lines( ≡) between the two atoms. E. g. N≡N, H-C≡C-H etc.
FORMATION OF A COVALENT BOND: Formation of a covalent bond is favored by
( i) High ionisation enthalpy of the combining elements.
( ii) Nearly equal electron gain enthalpy and equal electro-negativities of combining elements.
( iii) High nuclear charge and small atomic size of the combining elements.
POLAR COVALENT BOND: The bond between two unlike atoms which differ in their affinities for electrons is said to be polar covalent bond. E. g. H-Cl
COORDINATE BOND: The bond formed when one sided sharing of electrons take place is called a coordinate bond. Such a bond is also known as dative bond. It is represented by an arrow( →) pointing towards the acceptor atom. E. g. H3N→BF3
Bond Length: Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule
Bond Angle: It is defined as the angle between the orbitals containing bonding electron pairs around the central atom in a molecule / complex ion
Bond Enthalpy: It is defined as the amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state.
Bond Order: In the Lewis description of covalent bond, the Bond Order is given by the number of bonds between the two atoms in a molecule
Resonance: whenever a single Lewis structure cannot describe a molecule accurately, a number of structures with similar energy, positions of nuclei, bonding and non-bonding pairs of electrons are taken as the canonical structures of the hybrid which describes the molecule accurately