Chemical bond: In a molecule, different atoms are held together by a force of attraction called chemical bond.

When two atoms come closer, the electrons of one atom come under the influence of the electrons and the nucleus of the other atom. The interaction might produce an attraction between the two atoms.

Types of Chemical Bonds. Atoms combine in order to complete their respective octets mainly in two ways:

(i)By complete transfer of electrons. The chemical bond so formed is known as electrovalent bond or ionic bond.

(ii) By sharing of electrons. There are two types of such bonds:

(a)covalent bond - shared electrons are contributed equally by both the combining atoms.

(b) coordinate or dative bond - shared electrons are contributed only by one of the atoms.

Lewis symbols or electron dot symbols. According to this shorthand notation, the symbol of an element stands for the nucleus as well as the electrons in the inner energy shells. Each of the electrons in the outermost shell is represented by a dot near the symbol of the element. In case of ions, the ionic charge is also shown along with the symbol. The Lewis Structures of molecules are made by a combination of Lewis symbols of atoms or ions in accordance with the mode of formation of bonds.