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Chapter: 12th Chemistry : p-Block Elements-I

p-Block Elements-I: Summary

The elements in which their last electron enters the 'p' orbital, constitute the p-block elements.

Summary

·           The elements in which their last electron enters the 'p' orbital, constitute the p-block elements.

·           The p-block elements have a general electronic configuration of  ns2, np1-6. The elements of each group have similar outer shell electronic configuration and differ only in the value of n (principal quantum number).

·           Generally on descending a group the ionisation energy decreases and hence the metallic character increases.

·           The ionisation enthalpy of elements in successive groups is higher than the corresponding elements of the previous group as expected.

·           As we move down the 13th group, the electronegativity first decreases from boron to aluminium and then marginally increases.

·           In p-block elements, the first member of each group differs from the other elements of the corresponding group.

·           In 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 allothropism

·           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 [K2SO4. Al2(SO4)3.24.H2O].

·           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 an 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 (R2SiO). Because of their very high thermal stability they are called high –temperature polymers.

·           The mineral which contains silicon and oxygen in tetrahedral [SiO4]4- 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 

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