Carbon is an extraordinarily versatile element. Although it accounts for only 0.02% of Earth's crust and 0.03% of the atmosphere, millions of carbon compounds exist — forming the structural foundation of all living matter, fuels, plastics, medicine, and food. Carbon and its Compounds forms Chapter 4 of the CBSE Class 10 Chemistry syllabus.
This comprehensive guide explores why carbon forms covalent bonds, allotropes of carbon, saturated vs unsaturated hydrocarbons, structural isomerism, functional groups, homologous series, key chemical reactions, ethanol and ethanoic acid, and the micelle cleansing action of soaps and detergents.
- 1. Covalent Bonding in Carbon — Why Carbon Shares Electrons
- 2. Allotropes of Carbon — Diamond, Graphite & Fullerene
- 3. Hydrocarbons: Saturated (Alkanes) & Unsaturated (Alkenes, Alkynes)
- 4. Structural Isomerism & Hydrocarbon Chains
- 5. Functional Groups & Homologous Series
- 6. Chemical Properties & Reactions of Carbon Compounds
- 7. Important Compounds: Ethanol & Ethanoic Acid
- 8. Soaps, Detergents & Micelle Cleansing Mechanism
- 9. Solved Board Exam Questions
- 10. Frequently Asked Questions (FAQ)
1. Covalent Bonding in Carbon — Why Carbon Shares Electrons
Carbon has atomic number 6 with electronic configuration (2, 4). To achieve noble gas stability (octet), it needs 4 electrons. However, carbon cannot form ionic bonds:
- Why not C⁰⁺ cation? Removing 4 electrons requires a colossal amount of energy that carbon's small nucleus cannot supply.
- Why not C⁰¯ anion? A nucleus with 6 protons cannot hold onto 10 electrons stably due to heavy inter-electronic repulsion.
Therefore, carbon overcomes this problem by SHARING its 4 valence electrons with other atoms, forming strong covalent bonds.
2. Tetravalency: Since carbon has a valency of 4, it is capable of bonding with four other atoms of carbon, hydrogen, oxygen, nitrogen, or halogens.
2. Allotropes of Carbon — Diamond, Graphite & Fullerene
Allotropy is the property by which an element can exist in two or more different physical forms having similar chemical properties but different physical structures.
| Property | Diamond | Graphite | Buckminsterfullerene (C₆⁰) |
|---|---|---|---|
| Bonding Structure | Each carbon bonded to 4 other carbons in a rigid 3D tetrahedral network | Each carbon bonded to 3 other carbons in 2D hexagonal layers held by weak Van der Waals forces | Carbon atoms joined in a hollow spherical geodesic dome shape (soccer ball layout) |
| Hardness & Density | Hardest naturally occurring substance; very high density | Soft, smooth, and slippery to touch (layers slide over each other) | Dark solid at room temperature |
| Electrical Conductivity | Non-conductor (No free mobile electrons) | Good conductor of electricity (1 free delocalized electron per carbon atom) | Semiconductor behavior under specific conditions |
| Primary Uses | Cutting glass, rock drilling bits, jewelry, precision surgical knives | Pencil lead, solid lubricant in heavy machinery, battery electrodes | Nanotechnology, drug delivery, catalysts |
3. Hydrocarbons: Saturated (Alkanes) & Unsaturated (Alkenes, Alkynes)
Compounds composed exclusively of Carbon and Hydrogen are called Hydrocarbons.
| Hydrocarbon Type | Bonding | General Formula | First 3 Members | Reactivity & Flame |
|---|---|---|---|---|
| Alkanes (Saturated) | Single C−C bonds | CₙH₂ₙ⁺₂ | Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈) | Relatively unreactive (paraffins); burn with clean blue flame |
| Alkenes (Unsaturated) | Double C=C bond | CₙH₂ₙ | Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈) | Highly reactive; burn with yellow smoky soot flame |
| Alkynes (Unsaturated) | Triple C≡C bond | CₙH₂ₙ⁻₂ | Ethyne / Acetylene (C₂H₂), Propyne (C₃H₄), Butyne (C₄H₆) | Very reactive; ethyne + oxygen used in oxy-acetylene welding |
4. Structural Isomerism & Hydrocarbon Chains
Structural Isomers are compounds having the same molecular formula but different structural arrangements of carbon atoms.
1. n-Butane: Straight 4-carbon chain (CH₃−CH₂−CH₂−CH₃).
2. Iso-butane (2-Methylpropane): Branched 3-carbon chain with methyl group at C-2 [CH₃−CH(CH₃)−CH₃].
Note: Pentane (C₅H₁₂) has 3 structural isomers: n-pentane, isopentane, and neopentane.
5. Functional Groups & Homologous Series
A Functional Group is an atom or group of atoms attached to a carbon chain that determines the chemical properties of the organic compound.
| Heteroatom / Family | Functional Group Name | Formula | Example Compound & IUPAC Name |
|---|---|---|---|
| Halogen (Cl, Br, I) | Halo group | −Cl, −Br | Chloroethane (C₂H₅Cl) |
| Oxygen | Alcohol | −OH | Ethanol (C₂H₅OH) |
| Oxygen | Aldehyde | −CHO | Ethanal (CH₃CHO) |
| Oxygen | Ketone | >C=O | Propanone / Acetone (CH₃COCH₃) |
| Oxygen | Carboxylic Acid | −COOH | Ethanoic Acid (CH₃COOH) |
1. Successive members differ by a −CH₂− unit in molecular formula.
2. Successive members differ by 14 u in molecular mass.
3. All members can be represented by the same general formula.
4. Show similar chemical properties but gradual gradation in physical properties (melting point, boiling point increase with mass).
6. Chemical Properties & Reactions of Carbon Compounds
C + O₂ → CO₂ + Heat + Light
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
Saturated hydrocarbons burn with clean blue flame; unsaturated hydrocarbons burn with yellow soot flame due to unburnt carbon particles.
CH₃CH₂OH [Ethanol] + 2[O] → CH₃COOH [Ethanoic Acid] + H₂O
Unsaturated Vegetable Oil + H₂ → Saturated Vegetable Ghee (Vanaspati Ghee)
Healthy cooking oils contain unsaturated fatty acids!
CH₄ + Cl₂ → CH₃Cl [Chloromethane] + HCl
7. Important Compounds: Ethanol & Ethanoic Acid
• Reaction with Sodium: 2Na + 2C₂H₅OH → 2C₂H₅ONa [Sodium Ethoxide] + H₂↑ (effervescence of H₂ gas).
• Dehydration to Ethene: Heating ethanol at 443 K with excess concentrated H₂SO₄ (dehydrating agent):
CH₃CH₂OH → CH₂=CH₂ [Ethene] + H₂O
ETHANOIC ACID (CH₃COOH / Acetic Acid): 5-8% solution in water is called Vinegar. Pure ethanoic acid freezes at 290 K (17°C) forming ice-like crystals → called Glacial Acetic Acid.
• Esterification Reaction: Ethanoic acid reacts with ethanol in presence of acid catalyst to form sweet-smelling Ester (Ethyl Ethanoate):
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ [Ester] + H₂O
• Saponification Reaction: Heating ester with sodium hydroxide base converts it back to alcohol and sodium salt of carboxylic acid (soap):
CH₃COOC₂H₅ + NaOH → CH₃COONa [Soap] + C₂H₅OH
• Reaction with Carbonates: Releases brisk effervescence of CO₂ gas:
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑
8. Soaps, Detergents & Micelle Cleansing Mechanism
Soap is a sodium or potassium salt of long-chain carboxylic acids (e.g., Sodium Stearate C₁⁷H₃₅COONa).
1. Hydrophobic Tail (Long Hydrocarbon Chain): Water-repelling, oil-loving. Dissolves in dirt/grease.
2. Hydrophilic Head (Ionic −COO¯Na⁺ End): Water-loving. Dissolves in water.
Micelle Formation: In water, soap molecules arrange themselves into spherical clusters called Micelles. The hydrophobic hydrocarbon tails cluster inside pointing towards the central oily dirt drop, while the hydrophilic ionic heads point outwards into water. When rinsed, the micelle containing trapped oily dirt is easily washed away.
Soaps vs Synthetic Detergents in Hard Water:
Hard water contains dissolved Ca²⁺ and Mg²⁺ salts. When soap is added to hard water, it reacts with these calcium and magnesium ions to form an insoluble sticky white precipitate called Scum, wasting soap.
Synthetic Detergents (ammonium or sulphonate salts of long-chain carboxylic acids) do NOT form scum with Ca²⁺ and Mg²⁺ ions and cleanse effectively in both soft and hard water!
9. Solved Board Exam Questions
Two versatile properties: (1) Catenation (self-linking ability to form long C-C chains) and (2) Tetravalency (capacity to bond with 4 other monovalent atoms).
(1) n-Butane: CH₃−CH₂−CH₂−CH₃ (straight chain)
(2) 2-Methylpropane (Isobutane): CH₃−CH(CH₃)−CH₃ (branched chain)
Equation: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ (Ethyl Ethanoate) + H₂O
Conversion back to alcohol: By Saponification (heating ester with alkali like NaOH):
CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH.
Industrial Application: Used to convert liquid unsaturated vegetable oils into solid saturated fats (Vanaspati Ghee).
In Hard Water: Hard water contains Ca²⁺ and Mg²⁺ ions which react with soap to form an insoluble sticky precipitate called Scum, making soap ineffective.
Explore Related CBSE Class 9 & 10 Science Guides
10. Frequently Asked Questions (FAQ)
Carbon has 4 valence electrons. Losing 4 electrons to form C⁰⁺ requires an impossibly high amount of ionization energy, while gaining 4 electrons to form C⁰¯ creates unstable electron-electron repulsion that 6 protons cannot hold. Hence, carbon shares electrons to form covalent bonds.
A Homologous Series is a group of organic compounds sharing the same functional group and general formula. Two key characteristics: (1) Adjacent members differ by a −CH₂− formula unit and 14 u molecular mass. (2) Members exhibit similar chemical properties.
Esterification: Reaction of a carboxylic acid with an alcohol in presence of acid catalyst to form a sweet-smelling Ester.
Saponification: Reaction of an ester with a strong base (like NaOH) to form soap (sodium salt of carboxylic acid) and alcohol.
In Graphite, each carbon atom is bonded to only 3 other carbon atoms, leaving 1 free delocalized electron per carbon to conduct electricity. In Diamond, each carbon is bonded to 4 other carbons in a rigid 3D lattice with no free electrons.
Soaps react with Ca²⁺ and Mg²⁺ ions in hard water to form an insoluble sticky scum that wastes soap. Synthetic detergents do not form scum with hard water ions and create rich lather to clean effectively in both hard and soft water.
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