Chapter 4: Carbon and Its Compounds

Introduction

Carbon is one of the most versatile elements known, forming the basis of all life on Earth. It is present in a vast number of compounds, from the simplest gas, carbon dioxide (CO₂), to the complex molecules of life like proteins, carbohydrates, and DNA. Its unique property of forming covalent bonds, along with its ability to bond with a variety of other elements, particularly hydrogen, oxygen, and nitrogen, makes it a fundamental building block of nature. Carbon’s diversity in bonding also gives rise to a whole branch of chemistry known as Organic Chemistry, which deals with carbon-containing compounds. Understanding carbon and its compounds is critical, as it extends to fuels, plastics, medicines, and the food we eat.

Key Terms

• Catenation: The ability of carbon to form bonds with other carbon atoms to form chains.
• Hydrocarbons: Compounds composed entirely of carbon and hydrogen.
• Saturated Hydrocarbons (Alkanes): Hydrocarbons where carbon atoms are bonded by single bonds.
• Unsaturated Hydrocarbons: Hydrocarbons with one or more double or triple bonds between carbon atoms (Alkenes and Alkynes).
• Isomerism: Compounds with the same molecular formula but different structural arrangements.
• Homologous Series: A series of compounds where each member differs from the previous one by a CH₂ group.
• Functional Group: An atom or group of atoms that replaces hydrogen in a hydrocarbon and defines the chemical properties of the molecule.
• Esterification: The chemical reaction between an alcohol and an acid to form an ester.
• Saponification: The process of soap formation by the reaction of an ester with a base.

Bonding in Carbon

Carbon atoms form covalent bonds. A covalent bond is formed by the sharing of electrons between atoms. The reason carbon forms covalent bonds rather than ionic bonds is because it has four electrons in its outer shell, and losing or gaining four electrons would require too much energy. Hence, carbon shares its electrons to achieve a stable electronic configuration.

Types of Covalent Bonds

1. Single Bond: When one pair of electrons is shared (e.g., Methane, CH₄).
2. Double Bond: When two pairs of electrons are shared (e.g., Ethene, C₂H₄).
3. Triple Bond: When three pairs of electrons are shared (e.g., Ethyne, C₂H₂).

Example: The simplest covalent compound, Methane (CH₄), forms by sharing four electrons with hydrogen atoms.

Catenation and Tetravalency

Carbon shows a unique property called Catenation. This is the ability of carbon to form long chains or rings by bonding with other carbon atoms. This property is due to the small size of carbon atoms and the strength of the C-C bond. The tetravalency of carbon allows it to form four covalent bonds with other atoms (including other carbon atoms), resulting in a wide variety of structures such as chains, branched chains, and rings.

Example: Diamond and graphite are forms of carbon that exhibit different bonding structures due to catenation.

Saturated and Unsaturated Carbon Compounds

Carbon compounds are classified into saturated and unsaturated compounds based on the type of bond between the carbon atoms.

1. Saturated Compounds: In these compounds, the carbon atoms are connected by single covalent bonds. These are also called alkanes. The general formula for alkanes is CₙH₂ₙ₊₂.

Example: Methane (CH₄), Ethane (C₂H₆).

2. Unsaturated Compounds: In these compounds, the carbon atoms are connected by double or triple covalent bonds. These are called alkenes (double bonds) or alkynes (triple bonds). The general formula for alkenes is CₙH₂ₙ and for alkynes is CₙH₂ₙ₋₂.

Example: Ethene (C₂H₄) – Alkene, Ethyne (C₂H₂) – Alkyne.

Daily Life Example: Cooking oil is an example of unsaturated fat (contains double bonds), whereas butter is an example of saturated fat (contains single bonds).

Chains, Branches, and Rings of Carbon Compounds

Carbon compounds can be arranged in:

• Straight Chains: Continuous carbon atoms linked in a straight line (e.g., Butane, C₄H₁₀).
• Branched Chains: Carbon chains with one or more branches (e.g., Iso-butane, C₄H₁₀).
• Rings: Carbon atoms form a closed structure (e.g., Cyclohexane, C₆H₁₂).

Daily Life Example: Glucose, which is vital for energy in our bodies, can exist in a straight chain or ring form.

Functional Groups in Carbon Compounds

Carbon compounds can contain additional atoms or groups of atoms called functional groups that determine the properties and reactions of these compounds. Some common functional groups include:

• Alcohol (-OH): Found in ethanol (C₂H₅OH), used in alcoholic beverages.
• Aldehyde (-CHO): Found in formaldehyde (HCHO), used as a preservative.
• Carboxylic Acid (-COOH): Found in acetic acid (CH₃COOH), used in vinegar.
• Ketone (C=O): Found in acetone (CH₃COCH₃), used as a solvent.
• Haloalkane (-X): Where X can be Cl, Br, or I, found in chloroform (CHCl₃).

Daily Life Example: Vinegar contains acetic acid, a common carboxylic acid.

Homologous Series

The homologous series is a group of organic compounds with a similar general formula, chemical properties, and a successive difference of a CH₂ group. The members of a homologous series show a gradation in physical properties like boiling point, melting point, and solubility.

Example of a Homologous Series: Alkanes

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)

Chemical Properties of Carbon Compounds

1. Combustion: Carbon compounds burn in the presence of oxygen to produce carbon dioxide, water, and energy. This is why hydrocarbons are used as fuels.

Example: Combustion of methane:

CH4​+2O2​→CO2​+2H2​O+Energy

2. Oxidation: Organic compounds can be oxidized to form alcohols, aldehydes, ketones, or carboxylic acids.
3. Addition Reaction: In unsaturated hydrocarbons (alkenes and alkynes), additional atoms can be added across double or triple bonds.

Example: The hydrogenation of vegetable oils to form margarine.

4. Substitution Reaction: In saturated hydrocarbons, one or more hydrogen atoms are replaced by another atom or group of atoms. This type of reaction is characteristic of alkanes due to their stable nature.

Example: When methane reacts with chlorine in the presence of sunlight, a substitution reaction occurs, replacing hydrogen atoms with chlorine atoms.

CH4​+Cl2  → ​UV→   ​CH3​Cl+HCl

Some Important Carbon Compounds

Ethanol (C₂H₅OH)

Ethanol, commonly known as alcohol, is a colorless liquid and an important industrial chemical used in beverages, medicines, and as a solvent. It can be obtained by fermentation of sugar in the presence of yeast.

Properties of Ethanol:

1. It is a liquid at room temperature with a boiling point of 78°C.
2. It is soluble in water.
3. It is used as a disinfectant, solvent, and fuel.

Daily Life Example: Ethanol is used in hand sanitizers and alcoholic beverages.

Ethanoic Acid (CH₃COOH)

Ethanoic acid, commonly known as acetic acid, is the main component of vinegar. It is a colorless liquid with a strong pungent smell and sour taste.

Properties of Ethanoic Acid:

1. It reacts with alcohols to form esters in the presence of an acid catalyst (esterification).
2. It reacts with bases to form salts (neutralization).
3. It can undergo oxidation to form carbon dioxide and water.

Example Reaction: Reaction of ethanoic acid with sodium bicarbonate (baking soda):

CH3​COOH+NaHCO3​→CH3​COONa+CO2​+H2​O

This reaction produces carbon dioxide gas, which is the basis of its use in baking powders.

Soap and Detergents

Soaps are sodium or potassium salts of long-chain fatty acids (e.g., stearic acid). They are made by the process of saponification, which involves the hydrolysis of fats and oils with a base (like NaOH or KOH).

Saponification Reaction:

C17​H35​COOH+NaOH→C17​H35​COONa+H2​O

(Stearic acid + Sodium hydroxide → Sodium stearate (Soap) + Water)

How Soap Works: Soap molecules have two ends:

• A hydrophilic (water-attracting) head.
• A hydrophobic (water-repelling) tail.

When soap is used with water, the hydrophobic tails surround oily dirt, forming structures called micelles, trapping the oil in the center, which can then be washed away with water.

Daily Life Example: Soap is used in daily hygiene to clean dirt and oils from the skin.

Difference Between Soap and Detergents

1. Soaps are biodegradable, while detergents are not easily biodegradable.
2. Soaps do not work well in hard water, whereas detergents can function effectively in hard water.

Cleansing Action of Soap

Soaps and detergents are used to remove dirt, especially from fabrics. When used in water, they lower the surface tension of the water, allowing it to interact more effectively with oily dirt. The hydrophobic end of soap attaches to oil, while the hydrophilic end remains in water, pulling away the dirt and grease, allowing them to be rinsed away.

Nomenclature of Carbon Compounds

The naming of carbon compounds follows the rules set by the International Union of Pure and Applied Chemistry (IUPAC). For alkanes, the naming is based on the number of carbon atoms in the molecule.

Isomerism

Isomers are compounds that have the same molecular formula but different structural arrangements. This phenomenon is called isomerism. There are several types of isomerism, but the most common in carbon compounds is structural isomerism, where the arrangement of atoms in the molecule is different.

Example: Butane (C₄H₁₀) has two isomers:

• n-Butane: A straight-chain hydrocarbon.
• Iso-butane: A branched-chain hydrocarbon.

Chemical Properties of Carbon Compounds

1. Combustion: Carbon and its compounds burn in the presence of oxygen to release carbon dioxide, water, and energy. This is the basis of carbon compounds being used as fuels.

Example: The combustion of methane:

CH4+2O2→CO2+2H2O+EnergyCH₄ + 2O₂ → CO₂ + 2H₂O + EnergyCH4​+2O2​→CO2​+2H2​O+Energy

2. Oxidation: Alcohols can be oxidized to form aldehydes and further to acids using oxidizing agents like potassium permanganate (KMnO₄).

Example: Ethanol is oxidized to form ethanoic acid:

C2H5OH+[O]→CH3COOH+H2O

3. Addition Reaction: Unsaturated hydrocarbons undergo addition reactions where atoms are added across double or triple bonds.

Example: The hydrogenation of vegetable oils to form saturated fats:

R−CH=CH−R+H2→R−CH2−CH2−R

4. Substitution Reaction: In saturated hydrocarbons, one or more hydrogen atoms are replaced by another atom or group.

Example: Methane reacts with chlorine in the presence of sunlight:

CH4+Cl2→UV→CH3Cl+HCl

Esterification and Saponification

1. Esterification: An ester is formed when a carboxylic acid reacts with an alcohol in the presence of an acid catalyst. Esters are sweet-smelling compounds used in perfumes and flavorings.

Example: Ethanoic acid reacts with ethanol to form ethyl ethanoate:

CH3COOH+C2H5OH→H2SO4→CH3COOC2H5+H2O

2. Saponification: This is the process by which soap is formed. It occurs when a fat or oil (ester) reacts with a strong base like sodium hydroxide to form soap and glycerol.

Example: Reaction of stearic acid with sodium hydroxide:

C17H35COOH+NaOH→C17H35COONa+H2O

Conclusion

The study of carbon and its compounds opens up a vast and fascinating area of chemistry. From fuels to medicines, plastics to perfumes, the versatility of carbon makes it an essential element in our everyday lives. By understanding the various properties and reactions of carbon compounds, we not only appreciate the chemical diversity around us but also learn to harness these compounds for various applications in industry, healthcare, and technology.

These notes have covered the essential aspects of carbon compounds as per the CBSE syllabus, enriched with daily life examples and comprehensive explanations of each concept. They should serve as a complete guide for mastering the topic of Carbon and Its Compounds in Class 10 Science.