This video lecture from Group IIIA and Group IVA Elements (F.Sc. second year Chemistry) covers the structure of crystalline silica or quartz. In silica, silicon is covalently bonded to four oxygen atom forming a tetrahedron. Each oxygen atom makes two covalent bonds with silicon. Silica forms trigonal crystal system. The inability of carbon to give a network giant structure like silica is discussed owing to its smaller size. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.