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
Catenation:
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.
Allotropism:
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.
McAfee process:
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.
Silicates:
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 |
| Germanium | α-germanium, β-germanium |
| 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 |
| Oxygen | Dioxygen, ozone |
| Sulphur | Rhombus sulphur, monoclinic sulphur |
| Selenium | Red selenium, Gray selenium, Black selenium, Monoclinic selenium, |
| Tellurium | Amourphous & Crystalline |