If energy released by the attraction of two atoms is more than 42KJ/mol then it is considered a chemical bond. The attractive force which holds together the atoms or groups of atoms in a chemical species is known as chemical bond.
Atoms combine together to complete their outermost shell and to attain the configuration of noble gas which is a stable configuration.
Ionic bond or Electrovalent Bond
It is an electrostatic force of attraction between two oppositely charged ions. Ionic bonds are formed between two dissimilar atoms having a large difference in their electronegativity values. The electronic concept of this chemical bond was proposed by Kossel.
Conditions for formation of Ionic Compounds
- The electronegativity difference between combining atoms should be large.
- The atom which makes cation should have greater size and low ionization energy so that it can easily lose its outermost electron.
- The atom which forms anion should have small size and more electron affinity. Non metals owing to their small size and more electron affinity form ionic compounds with s block elements.
- Ionic crystals have high lattice energy.
Lattice energy is the most important energy term which is responsible for the formation of stable ionic bonds.
Lattice energy defined as
“Energy released when 1 mol of an ionic compound is formed by its constituent ions in gaseous state.”
Determination of Lattice Energy
There are two methods to determine lattice energy.
- Born Haber cycle (indirect method)
- Kapustinskii equation (direct method)
Born Haber Cycle
This method is based on Hess law. For example NaCl is formed by two methods.
By Hess law,
Factor Affecting Lattice Energy
From Kapustinskii relation we have
According to Lewis, “Covalent bonds are formed from the sharing of the same number of electrons between two atoms.”
It is defined as the internuclear distance between two covalently bonded atoms.
The number of bonds present between two covalently bonded atoms is called bond order.
Fajans rules offer simple if inexact approaches to the problem of partial covalent character in ionic compounds. Fajans considered the effect which a small , highly charged cation would have on an anion.
low positive charge
high positive charge
The tendency of atoms to react in ways that achieve an outer shell of eight valence electrons is particularly common among Group 1A-7A elements and is given the special name of the octet rule.
The dipole moments are parallel and perpendicular to the distance R. The magnetic energy becomes
Hydrogen bonding occurs when a hydrogen atom is bonded to a small, highly electronegative atom, such as nitrogen, oxygen, or fluorine. The partial positive hydrogen is attracted to the partial negative nitrogen, oxygen, or fluorine of another molecule.
Metallic Bonding The bonding which holds the metal atoms firmly together on account of force of attraction between metal ions and the mobile electron is called metallic bonding.
A strong force of attraction holding atoms together in a molecule or crystal. A bond is a force which holds atoms together. When atoms come together to form compounds and molecules the atoms gain a more stable configuration of electrons.