A chemical bond may be defined as the force existing between two atoms or a group of atoms holding them together to keep their independent existence as an aggregate or a molecule.
Why do atoms combine to form molecules?
The classical concept of the formation of molecules is based upon the electronic structure of atoms. The atoms of inert gases have either 2 or 8 electrons in their outermost orbit. These gases don’t enter into the chemical combination and therefore are assumed to have complete or stable orbits.
The atoms of all other elements have incomplete outermost orbitals and tend to complete them by chemical combination with other atoms. It is the urge of the atoms to complete their outermost orbits of electrons as in the inert gases, which is responsible for chemical combination.
The chemical bond formation, atoms interact by losing, gaming on sharing of electrons to acquire a stable noble gas electronic configuration.
Types of Chemical Bond:
There are three ways in which chemical combination occurs:
1. Ionic Bond: They are formed by the transfer of valence electrons from one atom to another. This type of bond units atoms. One of which has more electrons than the stable number (2 or 8) and the other has fewer electrons than the stable number.
2. Covalent Bond: Covalent bonds are formed by the mutual sharing of electrons. This type of bond units two atoms both of which are short of electrons in comparison with the electronic configuration of inert gases. In Covalent compounds, molecules are held together by weak VanderWaal’s forces of attraction. These bonds are commonly found in organic compounds.
3. Coordinate Covalent Bond: It is also formed by mutual sharing of electrons but in this case the two electrons that are shared come from the same atom. A co-ordinate bond units are two atoms, one of which has a spare pair of electrons and the other is short of a pair of electrons. The first atom (donor) contributes one pair (lone pair) of electrons and the 2nd atom (acceptor) accepts it. After the formation of the bond, the lone pair is held in common. The co-ordinate bond is represented by an arrow pointing towards the acceptor from the donor atom.
Example: SO2, H2SO4