State the reasons for chemical bonding between two atoms and the methods involved for achieving the same. State how 'duplet and octet' rules are involved for an atom to achieve stable electronic configuration.

State the force which holds two or more atoms together as a stable molecule.

State why noble gases are unreactive while atoms of elements other than noble gases are chemically reactive.

Draw the geometrical atomic structure representing the electronic configuration of atoms of elements of :

1. Period-2
   1. group 14 [IVA] — carbon [at no. 6]
   2. group 15 [VA] — nitrogen [at. no. 7]
   3. group 16 [VI A] — oxygen [at no. 8]
2. Period-3
   1. group 1[IA] — sodium [at no. 11]
   2. group 2[IIA] — magnesium [at. no. 12]
   3. group 17[VIIA]— chlorine [at. no. 17]
3. Period-4
   1. group 2[IIA] — calcium [at. no. 20].