Grade 12
  1. Solid state  1.1. Classification of solids  1.2. Crystal Lattice and Unit Cell  1.3. Packing Efficiency  1.4. Density of unit cell  1.5. Imperfections in solids (point and line defects)  1.6. Electrical Properties of Solids (Conductors, Insulators and Semiconductors)  1.7. Magnetic Properties of Solids (Diamagnetic, Paramagnetic and Ferromagnetic Materials)
  2. Solution  2.1. Types of Solutions (Homogeneous and Heterogeneous)  2.2. Expressing concentration of solutions (mass %, volume %, molarity, molality, normality, mole fraction)  2.3. Solubility of solids and gases in liquids (Henry's law)  2.4. Raoult's Law and Ideal and Non-Ideal Solutions  2.5. Syndrome properties  2.6. Abnormal molar mass and Van't Hoff factor
  3. Electrochemistry  3.1. Electrochemical cells (galvanic and electrolytic cells)  3.2. Galvanic cell and EMF of the cell  3.3. Standard electrode potential and electrochemical series  3.4. Nernst equation and its applications  3.5. Conductivity and electrolytic cells (specific, molar and equivalent conductivity)  3.6. Kohlrausch's law and its applications  3.7. Batteries (primary and secondary cells)  3.8. Corrosion and its prevention
  4. Chemical kinetics  4.1. Rate of chemical reaction  4.2. Factors affecting the reaction rate (concentration, temperature, catalyst, surface area)  4.3. Order and molecularity of the reaction  4.4. Integrated Rate Equations (Zero, First and Second Order)  4.5. Half-life of a reaction  4.6. Collision theory and activation energy  4.7. Arrhenius equation and its applications
  5. Surface chemistry  5.1. Adsorption and its types (Physicosorption and Chemisorption)  5.2. Catalysis and its types (homogeneous and heterogeneous)  5.3. Colloids and their properties (Tyndall effect, Brownian motion, coagulation)  5.4. Emulsions and gels  5.5. Applications of Colloids
  6. General principles and processes of separation of elements  6.1. Presence of metals and minerals  6.2. Concentration of ores (gravity separation, froth flotation, magnetic separation)  6.3. Extraction of raw metals (roasting, calcination, reduction)  6.4. Thermodynamic and electrochemical principles of metallurgy  6.5. Refining of metals
  7. P-block elements  7.1. Group 15 elements (nitrogen and phosphorus)  7.2. Group 16 Elements (Oxygen, Sulphur and their Compounds)  7.3. Group 17 Elements (Halogens and their Compounds)  7.4. Group 18 Elements  7.5. Properties and Trends in p-Block Elements  7.6. Important compounds of p-block elements (ammonia, phosphine, sulphuric acid, hydrochloric acid)  7.7. Interhalogen compounds and their applications
  8. d-block and f-block elements  8.1. General Properties of Transition Metals  8.2. Properties of Inner Transition Metals (Lanthanoids and Actinoids)  8.3. Lanthanoid and actinoid contractions  8.4. Coordination Chemistry of d-Block Elements
  9. Coordination compounds  9.1. Werner's theory and modern concepts  9.2. Coordination number and type of ligand  9.3. Nomenclature of Coordination Compounds  9.4. Isomerism (geometrical and optical) in coordination compounds  9.5. Bonding in Coordination Compounds (Valence Bond Theory and Crystal Field Theory)  9.6. Stability and applications of coordination compounds in medicine and industry
  10. Haloalkanes and haloarenes  10.1. Classification and nomenclature of haloalkanes and haloarenes  10.2. Physical and Chemical Properties of Haloalkanes and Haloarenes  10.3. Mechanism of Nucleophilic Substitution Reactions (SN1 and SN2)  10.4. Uses and environmental effects (ozone depletion, CFCs)
  11. Alcohol, phenol and ether  11.1. Structure and classification of alcohols, phenols and ethers  11.2. Preparation and properties of alcohols  11.3. Preparation and properties of phenol  11.4. Preparation and properties of ethers  11.5. Chemical Reactions and Uses
  12. Aldehydes, ketones and carboxylic acids  12.1. Structure and nomenclature in aldehydes, ketones and carboxylic acids  12.2. Preparation and properties of aldehydes and ketones  12.3. Chemical reactions in aldehydes, ketones and carboxylic acids (nucleophilic addition, oxidation and reduction)  12.4. Preparation and Properties of Carboxylic Acids  12.5. Chemical Reactions and Uses of Carboxylic Acids
  13. Nitrogen-containing organic compounds  13.1. Amines (classification, structure, basicity)  13.2. Preparation and properties of amines  13.3. Reactions of Amines (Diazotization, Carbylamine Reaction)  13.4. Diazonium salts and their applications in paint industry
  14.1. Carbohydrates (classification and properties)  14.2. Proteins (Structure and Function)  14.3. Enzymes (Mechanism and Function)  14.4. Nucleic acids (DNA and RNA)  14.5. Vitamins and hormones
  15. Polymer  15.1. Classification of Polymers (Addition, Condensation, Copolymers)  15.2. Types of polymerization (free radical, ionic, condensation)  15.3. Important Polymers and Their Uses  15.4. Biodegradable and non-biodegradable polymers
  16. Chemistry in Everyday Life  16.1. Drugs and their classification (analgesics, antipyretics, antibiotics, antacids)  16.2. Chemicals in food and cosmetics (preservatives, artificial sweeteners, antioxidants)  16.3. Cleaning agents and detergents (soaps, synthetic detergents, surfactants)  16.4. Environmental Chemistry (Pollution, Green Chemistry, Sustainable Chemistry)

Grade 12 → Polymer ↓


Types of polymerization (free radical, ionic, condensation)


Polymers are large molecules composed of repeating structural units known as monomers. The process of forming these polymers from monomers is known as polymerization. In chemistry, understanding the types of polymerization is important because it helps create different types of materials with different properties. The primary methods of polymerization include free radical polymerization, ionic polymerization, and condensation polymerization. This explanation will go deeper into each of these types, exploring their mechanisms and providing visual and text examples to enhance understanding.

Free radical polymerization

Free radical polymerization is one of the most common types of polymerization and is widely used for the synthesis of various types of polymers. It involves the polymerization process initiated by free radicals. A free radical is a molecule or atom that has an unpaired electron, making it highly reactive. This process consists of three main steps: initiation, propagation, and termination.

Initiation

This step involves generating free radicals that can initiate the polymerization process. It often involves the decomposition of a peroxide or azo compound, producing free radicals. The general reaction can be simplified as follows:

ROOR' 🡪 2R•

For example, benzoyl peroxide is a common initiator that decomposes to form a phenyl radical:

(C₆H₅CO)₂O₂ 🡪 2C₆H₅CO•

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Here, the free radical generated during initiation reacts with a monomer to form a new radical. This new radical then reacts with another monomer, continuing the chain process:

R• + CH₂=CH₂ 🡪 R-CH₂-CH₂•

This process continues, with the polymer chain growing, and more monomers reacting:

R-CH₂-CH₂• + n(CH₂=CH₂) 🡪 R-[CH₂-CH₂]ₙ•

Closure

In this step, the growth of the polymer chain is stopped. Termination can occur through different mechanisms such as combination or disproportionation. In combination two growing polymer chains join together:

R-[CH₂-CH₂]ₙ• + R'-[CH₂-CH₂]ₘ• 🡪 R-[CH₂-CH₂]ₙ-R'

Disproportionation involves the transfer of a hydrogen atom from one radical to another:

R-[CH₂-CH₂]ₙ-H + R'-[CH₂-CH₂]ₘ• 🡪 R-[CH₂-CH₂]ₙ + R'-(CH₂=CH-)ₘH

This illustration shows a free radical attacking a double bond in an ethene (ethylene) monomer.

Anionic polymerization

Ionic polymerization involves the growth of polymer chains through ionic active centers. This type of polymerization is further classified into cationic and anionic polymerization, both named based on the type of ion (cation or anion) that facilitates the process.

Cationic polymerisation

Cationic polymerization is catalyzed by an acid, which creates a positively charged ion that initiates the reaction. It generally works well with monomers containing electron-donating groups.

Initiation

This process begins with the formation of a carbocation through the reaction of a monomer with an acid:

R-OH + H⁺ 🡪 R⁺ + H₂O

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The carbocation reacts with another monomer to form a new carbocation, initiating a chain reaction:

R⁺ + CH₂=CH-R' 🡪 R-CH₂-CH(R')⁺

Closure

Termination occurs when the cationic chain is neutralized, usually involving reaction with a base or another anion:

R-CH₂-CH(R')⁺ + Base 🡪 R-CH₂-CH(R') + Base⁺
Cationic initiator

This representation shows the cationic initiator extending the polymer chain.

Anionic polymerisation

Anionic polymerization involves the use of negatively charged ions to initiate the polymerization. This method generally works well with monomers containing electron-withdrawing groups.

Initiation

The initial process begins with an anion, often a strong base or organometallic compound, attacking the monomer:

R⁻ + CH₂=CH-X 🡪 R-CH₂-CH(X)⁻

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Once the anionic center is created, it can react with additional monomers to form longer polymer chains:

R-CH₂-CH(X)⁻ + n(CH₂=CH-X') 🡪 R-[CH₂-CH(X)]ⁿ-CH(X')⁻

Propagation continues until the anionic end is quenched by protonation or another reaction:

R-[CH₂-CH(X)]ⁿ-CH(X')⁻ + H⁺ 🡪 R-[CH₂-CH(X)]ⁿ-CH(X')-H

This diagram shows the anionic site (green) that reacts to extend the polymer chain.

Condensation polymerization

Condensation polymerization is different from the previous two methods because it involves the formation of covalent bonds between monomers, with the removal of small molecules such as water or methanol. This type of polymerization is common in the production of materials such as polyester and nylon.

Mechanism

The process typically involves the reaction of two different types of functional groups to form a polymer, with smaller molecules emerging as byproducts. For example, making a polyester from a diacid and a diol involves the following reaction:

n HOOC-R-COOH + n HO-R'-OH 🡪 [OC-R-COO-R'-O]ₙ + 2n H₂O

Example: Manufacture of nylon

Nylon is made by reacting diamines with diacids. For example, the manufacture of nylon 6,6 involves hexamethylenediamine and adipic acid:

n H₂N-(CH₂)₆-NH₂ + n HOOC-(CH₂)₄-COOH 🡪 [NH-(CH₂)₆-NH-CO-(CH₂)₄-CO]ₙ + 2n H₂O

This sequence shows the joining of polymer blocks (blue and grey) and the formation of a bond with the elimination of a small molecule (red line).

Comparison of polymerization methods

Each polymerization method has its own advantages and applications, depending on the properties required in the final polymer product.

Free radical polymerization: Suitable for a wide range of monomers and offers a simple setup. It is particularly useful for vinyl monomers. The process can be easily started and stopped, giving good control over the molecular weight of the polymer.

Ionic polymerization: Provides more control over the molecular weight distribution and can be used to make block copolymers. However, it requires harsh reaction conditions because the presence of moisture or impurities can disrupt the reaction.

Condensation polymerization: Ideal for producing step-growth polymers such as polyesters and polyamides. This generally requires high temperatures and long reaction times to reach high molecular weights.

Conclusion

Understanding free radical, ionic, and condensation polymerization is essential for chemists and materials scientists. These processes allow for the synthesis of a variety of polymers, each of which has unique properties and applications. Advances in polymerization techniques continue to invent new materials with wide applications, impacting industries around the world.

Dictionary

  • Radical: A molecule that has an unpaired electron, making it highly reactive.
  • Cation: A positively charged ion.
  • Anion: A negatively charged ion.
  • Monomer: A molecule that can react with other monomer molecules to form a polymer.
  • Polymer: Large molecules made of repeated subunits, called monomers.

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Types of polymerization (free radical, ionic, condensation)

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