MP Board Class 10 Science Chapter 4: Carbon and Its Compo…
MP Board Class 10 Science Chapter 4: Carbon and its Compounds — Carbon is the backbone of life on Earth. Every living organism contains carbon compounds, from DNA to proteins, carbohydrates to fats. This chapter explores the unique bonding properties of carbon, the vast world of hydrocarbons, functional groups, and the chemistry of everyday substances like ethanol and ethanoic acid. With an exam weightage of 8–12 marks, this is one of the most important chapters in your Class 10 Science syllabus.
📑 Table of Contents
🔗 1. Bonding in Carbon — The Covalent Bond
Why Carbon Forms Covalent Bonds
Carbon has the atomic number 6, with the electronic configuration 2,4. It has four electrons in its valence shell and needs four more to achieve the stable noble gas configuration. However, carbon cannot gain four electrons (C⁴⁻ ion) because it would require tremendous energy — the nucleus with six protons cannot hold ten electrons. Similarly, losing four electrons (C⁴⁺) would also require too much energy. Therefore, carbon achieves stability through covalent bonding — sharing its valence electrons with other atoms.
Types of Covalent Bonds
📘 Key Fact: Carbon is unique because it can form stable bonds with itself (catenation) and with other elements like hydrogen, oxygen, nitrogen, sulphur, and halogens. This property gives rise to over 10 million known carbon compounds!
- Covalent compounds have low melting and boiling points because intermolecular forces (van der Waals forces) are weak compared to ionic bonds.
- They are generally poor conductors of electricity because they do not form ions.
- Covalent compounds are insoluble in water but soluble in organic solvents like carbon tetrachloride and benzene.
🧬 2. Versatile Nature of Carbon
Catenation — The Self-Linking Property
Catenation is the ability of an element to form long chains, branched chains, or rings by bonding with atoms of the same element. Carbon has the strongest catenation ability among all elements because the C—C bond is very strong (348 kJ/mol). This allows carbon to form compounds with chain lengths ranging from 2 to over 100,000 carbon atoms.
Tetravalency
Carbon has a valency of 4, meaning it can form four covalent bonds with other atoms. This tetravalency allows carbon to form single, double, and triple bonds, leading to a diverse range of compounds. The four bonds point to the corners of a tetrahedron, giving carbon compounds their three-dimensional structure.
⛽ 3. Hydrocarbons — Saturated and Unsaturated
Hydrocarbons are compounds made of only carbon and hydrogen. They are classified into two main categories based on the type of carbon-carbon bonds:
Saturated Hydrocarbons (Alkanes)
Saturated hydrocarbons contain only single bonds between carbon atoms. They are called alkanes and follow the general formula CₙH₂ₙ₊₂. Examples: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈). Alkanes are relatively unreactive and undergo substitution reactions.
Unsaturated Hydrocarbons (Alkenes and Alkynes)
Unsaturated hydrocarbons contain one or more double or triple bonds between carbon atoms. They are more reactive than alkanes and undergo addition reactions.
⚗️ 4. Functional Groups in Carbon Compounds
A functional group is an atom or group of atoms that determines the chemical properties of an organic compound. When a hydrogen atom in a hydrocarbon is replaced by a functional group, the resulting compound belongs to a specific family with characteristic properties.
📊 5. Homologous Series
A homologous series is a group of organic compounds that have the same functional group, similar chemical properties, and a regular gradation in physical properties. Each successive member differs by a —CH₂— unit (14 atomic mass units).
Characteristics of Homologous Series
- All members have the same functional group.
- Each member differs from the next by —CH₂— (CH₂ = 14 amu).
- Members show a gradual change in physical properties (melting point, boiling point increase with molecular mass).
- All members have similar chemical properties due to the same functional group.
- They can be represented by a general formula (e.g., CₙH₂ₙ₊₂ for alkanes).
🧪 6. Ethanol and Ethanoic Acid — Properties and Reactions
Ethanol (C₂H₅OH)
Ethanol is the most common alcohol, produced by the fermentation of sugars. It is the active component of alcoholic beverages and is also used as a solvent, fuel, and antiseptic.
Properties of Ethanol
- Physical: Colourless liquid, boiling point 78°C, completely miscible with water in all proportions, has a pleasant smell.
- Reaction with sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑ (Sodium ethoxide + Hydrogen gas)
- Dehydration: C₂H₅OH —(Hot conc. H₂SO₄, 170°C)→ C₂H₄ + H₂O (Ethene is formed)
- Oxidation: C₂H₅OH —(Alkaline KMnO₄ / Acidified K₂Cr₂O₇)→ CH₃COOH (Ethanoic acid)
- Esterification: CH₃COOH + C₂H₅OH —(Conc. H₂SO₄)→ CH₃COOC₂H₅ + H₂O (Ethyl acetate + Water)
Esterification Reaction — Ethanol reacts with ethanoic acid in the presence of concentrated H₂SO₄ to form ethyl acetate (an ester) and water. Esters are sweet-smelling compounds used in perfumes and flavouring agents.
Ethanoic Acid (CH₃COOH)
Ethanoic acid, commonly known as acetic acid, is the main component of vinegar (5–8% ethanoic acid in water). It is a weak carboxylic acid with a characteristic pungent smell and sour taste.
Properties of Ethanoic Acid
- Physical: Colourless liquid, boiling point 118°C, forms ice-like crystals below 17°C (hence called glacial acetic acid).
- Reaction with carbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂↑ + H₂O (CO₂ gas — test with limewater turning milky)
- Reaction with sodium bicarbonate: CH₃COOH + NaHCO₃ → CH₃COONa + CO₂↑ + H₂O (Effervescence seen)
- Reaction with NaOH: CH₃COOH + NaOH → CH₃COONa + H₂O (Neutralisation reaction)
- Reaction with ethanol: Forms ester (as described above in esterification).
🧼 7. Soaps and Detergents
How Soaps Work
Soaps are sodium or potassium salts of long-chain carboxylic acids. They are made by the saponification reaction — heating fat or oil with sodium hydroxide (NaOH):
Fat/Oil + NaOH —(Heat)→ Soap + Glycerol
(C₁₇H₃₅COO)₃C₃H₅ + 3NaOH → 3C₁₇H₃₅COONa + C₃H₅(OH)₃
Cleansing Action of Soap
A soap molecule has two ends: a hydrophilic head (ionic —COO⁻Na⁺) that is attracted to water, and a hydrophobic tail (long hydrocarbon chain) that is repelled by water but attracted to oil and grease. When soap is added to water, the hydrophobic tails attach to dirt and oil, forming micelles — spherical structures with the tails pointing inward and the heads pointing outward. The micelles are suspended in water and washed away, leaving the surface clean.