heavier post-transition metals, the outer s electrons (ns) have a tendency to remain inert and show reluctance to take part in the bonding, which is known as inert pair effect. Some elements exist in more than one crystalline or molecular forms in the same physical state. For example, carbon exists as diamond and graphite. This phenomenon is called allotropism Borax is a sodium salt of tetraboric acid.
It is obtained from colemanite ore by boiling its solution with sodium carbonate. Boric acid can be extracted from borax and colemanite. Boric acid has a two dimensional layered structure. The name alum is given to the double salt of potassium aluminium sulphate [K SO .
Al (SO ) . .H O]. Carbon is found in the native form as graphite. Silicon occurs as silica (sand and quartz crystal).
Silicate minerals and clay are other important sources for silicon. Catenation is the ability of an element to form chain of atoms Carbon nanotubes, another recently discovered allotropes, have graphite like tubes with fullerene ends. Silicones or poly siloxanes are organo silicon polymers with general empirical formula (R SiO). Because of their very high thermal stability they are called high –temperature polymers.
The mineral which contains silicon and oxygen in tetrahedral [SiO ] - units linked together in different patterns are called silicates. Types of Silicates: ▶ Ortho silicates (Neso silicates), Pyro silicate (or) Soro silicates), Cyclic silicates (or Ring silicates) ▶ Inosilicates : Chain silicates (or pyroxenes), Double chain silicates (or amphiboles): ▶ Sheet or phyllo silicates ▶ Three dimensional silicates (or tecto silicates) Zeolites are three-dimensional crystalline solids containing aluminium, silicon, and oxygen in their regular three dimensional framework. Zeolites act as a molecular sieve for the removal of permanent hardness of water - - - - EVALUATION Choose the correct answer: . An aqueous solution of borax is a) neutral b) acidic c) basic d) amphoteric .
Boric acid is an acid because its molecule (NEET) a) contains replaceable H + ion b) gives up a proton c) combines