The force which holds atoms together in a molecule is called a chemical bond.
(ii) Ionic bond:
An ionic bond is a bond formed by the complete transfer of electrons from one atom to another. The attraction that binds opposite charged ions together is called the Ionic bond.
(iii) Covalent bond:
The covalent bond is the bond formed by sharing of electrons. This sharing may be between two atoms, or 4 atoms, or 6 atoms. The first is a single bond. Ths second is Double bond and third is a triple bond.
(iv) Co-ordinate covalent bond:
Co-ordinate covalent bond is the bond formed by one-sided sharing i.e. both electrons forming a bond are supplied by one atom only. This bond is denoted by the arrow –>.