Grade 10 Chapter 9: Carbon Compounds

Introduction

Carbon is one of the most versatile elements in the periodic table. It forms the backbone of millions of compounds that are essential for life and modern civilization. From the proteins in our bodies to the plastics we use daily, carbon compounds are everywhere. This chapter explores the fascinating world of carbon chemistry, its unique bonding properties, and the diverse range of compounds it forms.

Carbon: A Versatile Element

The Uniqueness of Carbon

Carbon belongs to group IV in the periodic table with an electronic configuration of 2,4. The valency of carbon is 4, which means it can form four bonds with other atoms. This unique property allows carbon to:

• Form bonds with itself (catenation) creating chains, branches, and rings
• Bond with various elements like hydrogen, oxygen, nitrogen, sulfur, and halogens
• Create an enormous variety of compounds with different properties and applications

Carbon in the Living World

• The entire living kingdom is made from carbon-based compounds
• Carbon is the basic ingredient of our body
• Millions of molecules ranging from the small methane molecule to the extremely large DNA molecule are made from carbon
• Carbon forms the backbone of all essential biomolecules like carbohydrates, proteins, lipids, and nucleic acids

Properties of Carbon Compounds

Carbon compounds have distinctive properties that set them apart from inorganic compounds:

1. Low melting and boiling points: Most carbon compounds have relatively low melting and boiling points compared to inorganic compounds.

2. Poor conductivity: Carbon compounds are generally bad conductors of heat and electricity because they do not form ions.

3. Covalent bonding: The chemical bonds in carbon compounds do not produce ions, resulting in covalent bonds rather than ionic bonds.

Bonds in Carbon Compounds

Background of Bond Formation by Carbon

Carbon has 4 valence electrons and needs 4 more electrons to achieve the stable noble gas configuration of neon. To attain this stability, carbon shares its 4 valence electrons with other atoms, forming covalent bonds.

Carbon and Neon Configuration

• Carbon atoms share four valence electrons to attain neon configuration
• Shared electrons are accommodated in overlapping regions of valence shells, resulting in a noble gas configuration
• This route ensures atoms remain electrically neutral, promoting stability
• Therefore, carbon atoms adopt this route to attain a noble gas configuration

Covalent Bond

A covalent bond is formed by sharing two valence electrons between two atoms. In carbon compounds, covalent bonds are represented in several ways:

1. Electron-dot structure: A circle around the atomic symbol with each valence electron indicated by a dot or cross
2. Line structure: A small line joining the symbols of the two atoms represents a covalent bond

Types of Covalent Bonds

1. Single bond: One pair of shared electrons between atoms (e.g., H-H)
2. Double bond: Two pairs of shared electrons between atoms (e.g., O=O)
3. Triple bond: Three pairs of shared electrons between atoms (e.g., N≡N)

Hydrocarbons: Saturated and Unsaturated

Hydrocarbons are compounds composed only of carbon and hydrogen atoms. They are classified into two main categories:

Saturated Hydrocarbons (Alkanes)

• Contain only single bonds between carbon atoms
• General formula: CₙH₂ₙ₊₂
• Examples: methane (CH₄), ethane (C₂H₆), propane (C₃H₈)
• Relatively less reactive due to stable single bonds

Unsaturated Hydrocarbons

1. Alkenes
2. Contain at least one carbon-carbon double bond
3. General formula: CₙH₂ₙ
4. Examples: ethene (C₂H₄), propene (C₃H₆)

5. More reactive than alkanes due to the presence of double bonds

6. Alkynes

7. Contain at least one carbon-carbon triple bond
8. General formula: CₙH₂ₙ₋₂
9. Examples: ethyne (C₂H₂), propyne (C₃H₄)
10. Highly reactive due to the presence of triple bonds

Functional Groups in Carbon Compounds

A functional group is an atom or group of atoms that replaces hydrogen in a hydrocarbon and gives specific properties to the compound. The major functional groups include:

1. Alcohols (-OH)
2. General formula: R-OH (where R is an alkyl group)
3. Example: Ethanol (C₂H₅OH)

4. Properties: Soluble in water, higher boiling points than corresponding alkanes

5. Aldehydes (-CHO)

6. General formula: R-CHO
7. Example: Acetaldehyde (CH₃CHO)

8. Properties: Pleasant fruity smell, easily oxidized to carboxylic acids

9. Ketones (-CO-)

10. General formula: R-CO-R'
11. Example: Acetone (CH₃COCH₃)

12. Properties: Sweet smell, good solvents

13. Carboxylic Acids (-COOH)

14. General formula: R-COOH
15. Example: Acetic acid (CH₃COOH)

16. Properties: Sour taste, acidic nature, form esters with alcohols

17. Esters (-COO-)

18. General formula: R-COO-R'
19. Example: Ethyl acetate (CH₃COOC₂H₅)
20. Properties: Pleasant fruity smell, used in perfumes and flavorings

Homologous Series

A homologous series is a group of organic compounds having: - The same general formula - Similar chemical properties due to the same functional group - A gradual change in physical properties with increasing molecular mass - Consecutive members differing by a -CH₂- group

Examples of homologous series include: - Alkanes (CₙH₂ₙ₊₂) - Alcohols (CₙH₂ₙ₊₁OH) - Carboxylic acids (CₙH₂ₙ₊₁COOH)

Nomenclature of Carbon Compounds

The systematic naming of carbon compounds follows the IUPAC (International Union of Pure and Applied Chemistry) system:

1. Identify the longest carbon chain to determine the parent name (e.g., meth- for 1 carbon, eth- for 2 carbons)
2. Identify the functional group to determine the suffix (-ane for alkanes, -ene for alkenes, -ol for alcohols)
3. Number the carbon chain to give the functional group the lowest possible number
4. Name and number any substituents (e.g., methyl, ethyl) attached to the main chain

Examples: - CH₃-CH₂-CH₂-OH: Propan-1-ol - CH₃-CH(OH)-CH₃: Propan-2-ol - CH₃-CH₂-COOH: Propanoic acid

Chemical Properties of Carbon Compounds

Combustion

All carbon compounds burn in excess oxygen to form carbon dioxide and water, releasing heat and light: - CH₄ + 2O₂ → CO₂ + 2H₂O + Heat + Light

Oxidation

Alcohols can be oxidized to form aldehydes, ketones, and carboxylic acids: - Primary alcohols → Aldehydes → Carboxylic acids - Secondary alcohols → Ketones - Tertiary alcohols → Resistant to oxidation

Addition Reactions

Unsaturated hydrocarbons undergo addition reactions due to the presence of multiple bonds: - Hydrogenation: Addition of hydrogen (e.g., C₂H₄ + H₂ → C₂H₆) - Halogenation: Addition of halogens (e.g., C₂H₄ + Br₂ → C₂H₄Br₂)

Substitution Reactions

Saturated hydrocarbons undergo substitution reactions where hydrogen atoms are replaced by other atoms: - Halogenation: CH₄ + Cl₂ → CH₃Cl + HCl

Important Carbon Compounds: Ethanol and Ethanoic Acid

Ethanol (C₂H₅OH)

Properties: - Colorless liquid with a pleasant smell - Boiling point: 78°C - Miscible with water in all proportions - Intoxicating when consumed

Preparation: 1. Fermentation of sugars: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ 2. Industrial production from ethene: C₂H₄ + H₂O → C₂H₅OH

Uses: - As a solvent in medicines, perfumes, and cosmetics - As a fuel (gasohol - mixture of petrol and ethanol) - In the preparation of alcoholic beverages - As an antiseptic in medical wipes and hand sanitizers

Ethanoic Acid (CH₃COOH)

Properties: - Colorless liquid with a sour taste and pungent smell - Boiling point: 118°C - Miscible with water in all proportions - 5-8% solution in water is called vinegar

Preparation: 1. Oxidation of ethanol: C₂H₅OH + O₂ → CH₃COOH + H₂O 2. From acetaldehyde: CH₃CHO + [O] → CH₃COOH

Uses: - As vinegar in food preservation and flavoring - In the production of synthetic fibers and fabrics - In the preparation of esters used in perfumes - As a laboratory reagent

Macromolecules and Polymers

Polymers

Polymers are large molecules formed by the combination of many smaller molecules (monomers) through a process called polymerization.

Natural Polymers: - Proteins (made from amino acids) - Cellulose (made from glucose) - Starch (made from glucose) - Natural rubber (made from isoprene)

Synthetic Polymers: - Polyethylene (made from ethene) - PVC (made from vinyl chloride) - Nylon (made from diamines and dicarboxylic acids) - Bakelite (made from phenol and formaldehyde)

Importance of Polymers

Polymers have revolutionized modern life through their applications in: - Packaging materials - Clothing and textiles - Construction materials - Medical devices and implants - Electronics and insulation

Environmental Impact of Carbon Compounds

While carbon compounds have immense benefits, they also pose environmental challenges:

1. Plastic pollution: Non-biodegradable plastic waste accumulates in the environment
2. Greenhouse effect: Combustion of fossil fuels releases CO₂, contributing to global warming
3. Ozone depletion: Certain carbon compounds like CFCs damage the ozone layer

Sustainable Approaches

To address these challenges, sustainable approaches include: - Developing biodegradable polymers - Recycling plastic waste - Using renewable carbon sources - Implementing green chemistry principles

Summary

Carbon's unique ability to form covalent bonds with itself and other elements makes it the foundation of organic chemistry. The diverse range of carbon compounds, from simple hydrocarbons to complex polymers, plays a crucial role in our daily lives and industrial applications. Understanding the properties, reactions, and applications of carbon compounds is essential for developing sustainable technologies and addressing environmental challenges.

Practice Questions

1. Explain why carbon forms covalent bonds instead of ionic bonds.
2. Differentiate between saturated and unsaturated hydrocarbons with examples.
3. What are functional groups? Explain their role in determining the properties of carbon compounds.
4. Describe the process of fermentation and its importance in producing ethanol.
5. Explain the concept of homologous series with suitable examples.
6. How are addition reactions different from substitution reactions? Give examples.
7. Discuss the environmental impact of plastic polymers and suggest sustainable alternatives.
8. Explain the IUPAC system of nomenclature with examples of different carbon compounds.
9. Compare and contrast the properties and uses of ethanol and ethanoic acid.
10. Describe the formation of polymers and their significance in modern life.

References: 1. Maharashtra State Board 10th Standard Science Syllabus 2025-26 2. NCERT Science Textbook for Class 10 3. KitabCd Academy Notes on Carbon Compounds 4. Aakash Institute Science Materials for Maharashtra Board