Tamilnadu Samacheer Kalvi 12th Chemistry Notes Chapter 2 p-Block Elements-I Notes
p-Block elements have a general electronic configuration of ns2, np1-6
Carbon(atom) has a greater tendency to join a chain of bonds with itself or with other atoms which is known as catenation.
Inert pair effect:
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. This phenomenon is called allotropism.
Uses of boron:
- Boron isotope – 10B5 is used as moderator in nuclear reactions.
- Amorphous boron is used as a rocked fuel igniter.
- Boron is essential for the cell walls of plants.
Uses of boric acid:
- To manufacture of pottery glazes, glass, enamels and pigments.
- It is used as an antiseptic and as an eye lotion.
- It is also as a food preservative.
Uses of borax:
- Borax is used for the identification of coloured metal ions.
- In the manufacture optical and borosilicate glass, enamels and glazes for pottery.
- It is also used as a good preservative.
Hydroboration: Diborane adds on to alkenes and alkynes in ether solvent at room temperature. This reaction is called hydroboration.
Uses of diborane:
- It is used as a high energy fuel for propellant.
- It is used as a reducing agent in organic chemistry.
- It is used in welding torches.
Uses of boron trifluoride:
- BF3 is used for preparing HBF4, a catalyst in organic chemistry.
- It is also used a fluorinating reagent.
Aluminium chloride is obtained by heating a mixture of alumina and coke in a current of chlorine.
Uses of aluminium chloride:
- Anhydrous AlCl3 is used as a catalyst in friedel crafts reactions.
- It is used for the manufacture of petrol by cracking the mineral oils.
- It is used as a catalyst in the manufacture on dyes, drugs and perfumes.
Uses of Alum:
- It is used for purification of water.
- It is used for water proofing and textiles.
- It is employed as a styptic agent to arrest bleeding.
Fischer Tropsch synthesis:
The reaction of carbon monoxide with hydrogen at a pressure of less than 50 atm using metal catalysts at 500 – 700 K yields saturated and unsaturated hydrocarbons.
Uses of carbon monoxide:
- Equimolar mixture of hydrogen and carbon monoxide – water gas and the mixture of carbon monoxide and nitrogen – producer gas are important industrial fuels
- Carbon monoxide is a good reducing agent and can reduce many metal oxides to metals.
- Carbon monoxide is an important ligand and forms carbonyl compound with transition metals
Water gas equilibrium:
The equilibrium involved in the reaction between carbon dioxide and hydrogen, has many industrial application and is called water gas equilibrium.
Uses of carbon dioxide:
- Carbon dioxide is used to produce an inert atmosphere for chemical processing.
- Biologically, it is important for photosynthesis.
- It is also used as fire extinguisher and as a propellent gas.
- It is used in the production of carbonated beverages and in the production of foam.
Uses of Silicon tetrachloride:
- Silicon tetrachloride is used in the production of semiconducting silicon.
- It is used as a starting material in the synthesis of silica gel, silicic esters, a binder for ceramic materials.
Uses of Silicones:
- Silicones are used for low temperature lubrication and in vacuum pumps, high temperature oil baths etc…
- They are used for making water proofing clothes
- They are used as insulting material in electrical motor and other appliances
- They are mixed with paints and enamels to make them resistant towards high temperature, sunlight, dampness and chemicals.
The mineral which contains silicon and oxygen in tetrahedral [SiOJ4~ units linked . together in different patterns are called silicates.
Types of Silicates:
(i) Ortho silicates (ii) Pyro silicates (iii) Cyclic silicates (iv) Ino silicates (v) Phyllo silicates (vi) Tecto silicates.
Zeolites: Zeolites are three dimensional crystalline solids containing Al, Si and Oxygen in their regular three dimensional frame work. They are hydrated sodium alumino silicates.
Some of common allotropes of p-block elements
|Element||Most common allotropes|
|Boron||Amorphous boron, α-rhombohedral boron, β-rhombohedral boron, γ-orthorhombic boron, α-tetragonal boron, β-tetragonal boron|
|Carbon||Diamond, Graphite, Graphene, Fullerenes, Carbon nanotubes|
|Silicon||Amourphous silicon, crystalline silicon|
|Tin||Grey tin, white tin, rhombic tin, sigma tin|
|Phosphorous||White phosphorous, Red phosphorous, Scarlet phosphorous, Violet phosphorous, Black phosphorous.|
|Arsenic||Yellow arsenic, gray arsenic & Black arsenic|
|Antimony||Blue-white antimony, Yellow, Black|
|Sulphur||Rhombus sulphur, monoclinic sulphur|
|Selenium||Red selenium, Gray selenium, Black selenium, Monoclinic selenium,|
|Tellurium||Amourphous & Crystalline|