Carbon and its Compounds — Class 10 Science
"Carbon is the backbone of life. From your DNA to the petrol in your car — all carbon."
1. About the Chapter
This chapter introduces ORGANIC CHEMISTRY — the chemistry of CARBON COMPOUNDS. Carbon has 10 million+ known compounds — more than all other elements combined!
Topics
- Carbon's unique properties (catenation, tetravalency)
- Covalent bonding
- Hydrocarbons (saturated/unsaturated)
- Functional groups
- IUPAC nomenclature
- Some important compounds (ethanol, ethanoic acid)
- Soaps and detergents
Why Important
- Foundation for Class 11-12 organic chemistry
- All life uses carbon compounds
- Petrochemical industry
- Pharmaceuticals
- Plastics, fuels, foods
2. Carbon's Unique Properties
Tetravalency
Carbon has 4 valence electrons. It needs 4 more to complete octet. To do this, it FORMS 4 COVALENT BONDS with other atoms.
This is tetravalency — carbon makes 4 bonds.
Catenation
Carbon atoms can BOND TO OTHER CARBON ATOMS forming chains or rings. This unique ability is called CATENATION.
This is why carbon has MILLIONS of compounds.
Why Carbon is Special
- Tetravalency: makes 4 bonds (lots of variety)
- Catenation: long chains and rings possible
- Forms stable bonds with H, N, O, S, halogens
- All life is built on carbon
3. Covalent Bonding
What is It?
A covalent bond = SHARING of electrons between atoms.
Example: H₂
Two hydrogen atoms each have 1 electron. They SHARE 2 electrons: H · + · H → H : H (or H-H)
Example: H₂O (water)
Oxygen has 6 valence electrons; needs 2 more. Each H shares 1 electron with O.
Single, Double, Triple Bonds
- Single (-): 1 pair shared (CH₄)
- Double (=): 2 pairs shared (CO₂, C=C in alkenes)
- Triple (≡): 3 pairs shared (N₂, C≡C in alkynes)
Properties of Covalent Compounds
- Generally LOW melting/boiling points
- Mostly INSOLUBLE in water (some exceptions)
- Don't conduct electricity (no ions)
- Can be solid, liquid, or gas at room temp
4. Hydrocarbons
Definition
Compounds containing only HYDROGEN and CARBON.
Types
Saturated Hydrocarbons (ALKANES):
- Only SINGLE bonds between carbons
- Formula: CₙH₂ₙ₊₂
- Examples: CH₄ (methane), C₂H₆ (ethane), C₃H₈ (propane)
Unsaturated Hydrocarbons:
Alkenes (one C=C double bond):
- Formula: CₙH₂ₙ
- Examples: C₂H₄ (ethene/ethylene), C₃H₆ (propene)
Alkynes (one C≡C triple bond):
- Formula: CₙH₂ₙ₋₂
- Examples: C₂H₂ (ethyne/acetylene), C₃H₄ (propyne)
5. Naming Hydrocarbons (IUPAC)
Names of Carbon Chains
| Carbons | Name |
|---|---|
| 1 | Methane (meth-) |
| 2 | Ethane (eth-) |
| 3 | Propane (prop-) |
| 4 | Butane (but-) |
| 5 | Pentane (pent-) |
| 6 | Hexane (hex-) |
| 7 | Heptane (hept-) |
| 8 | Octane (oct-) |
| 9 | Nonane (non-) |
| 10 | Decane (dec-) |
Suffixes
- -ane: saturated (alkane), all single bonds
- -ene: alkene (one double bond)
- -yne: alkyne (one triple bond)
Examples
- 2-carbon alkane: ethane (C₂H₆)
- 2-carbon alkene: ethene (C₂H₄)
- 2-carbon alkyne: ethyne (C₂H₂)
- 4-carbon alkane: butane (C₄H₁₀)
- 4-carbon alkene: butene (C₄H₈)
6. Functional Groups
What is a Functional Group?
An ATOM or GROUP OF ATOMS that gives specific properties to a compound.
Important Functional Groups
| Functional Group | Suffix/Prefix | Example |
|---|---|---|
| Halogens (-Cl, -Br, -I, -F) | Prefix (chloro, bromo, etc.) | CH₃Cl (chloromethane) |
| Alcohol (-OH) | -ol | CH₃OH (methanol) |
| Aldehyde (-CHO) | -al | HCHO (methanal) |
| Ketone (-C=O-) | -one | CH₃COCH₃ (propanone/acetone) |
| Carboxylic acid (-COOH) | -oic acid | CH₃COOH (ethanoic acid/acetic acid) |
7. Important Compounds
Ethanol (CH₃CH₂OH or C₂H₅OH)
- 'Alcohol' in drinks
- Also called ethyl alcohol or grain alcohol
- Made by fermentation of sugars (yeast)
- Used in: alcoholic drinks, antiseptic (>70% kills germs), solvent, fuel
Properties:
- Colourless liquid
- Boiling point 78°C
- Miscible with water
- Burns: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
Ethanoic Acid (CH₃COOH or Acetic Acid)
- Common name: VINEGAR (dilute solution)
- 5-8% acetic acid solution in water = vinegar
Properties:
- Pungent smell
- Weak acid (pH ~3)
- Reacts with bases, carbonates
- Frozen below 16°C — 'glacial' acetic acid
8. Reactions of Ethanol
Combustion
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O (releases lots of energy)
Oxidation (with KMnO₄)
C₂H₅OH → CH₃COOH (alcohol becomes acid)
Dehydration (with H₂SO₄)
C₂H₅OH → C₂H₄ + H₂O (alcohol → alkene)
Esterification (with acid)
C₂H₅OH + CH₃COOH ↔ CH₃COOC₂H₅ + H₂O (produces 'ester' — fruity smell; used in perfumes)
9. Reactions of Ethanoic Acid
With Bases
NaOH + CH₃COOH → CH₃COONa + H₂O (sodium ethanoate)
With Carbonates
CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑
Esterification
CH₃COOH + C₂H₅OH ↔ CH₃COOC₂H₅ + H₂O (ester)
10. Soaps and Detergents
Soap
Sodium salt of long-chain fatty acid (R-COONa where R is long carbon chain).
How It Cleans
- Soap molecule has TWO parts:
- Hydrophobic tail (hydrocarbon — repels water, attaches to oil/dirt)
- Hydrophilic head (carboxylate — loves water)
- Forms MICELLES around dirt
- Water washes away the micelle
Limitation
Soap doesn't work well in HARD WATER (calcium, magnesium ions form precipitate — 'scum').
Detergents
Sodium salts of long-chain sulphonic acids or ammonium salts.
- Work in hard water
- More versatile
- Used in detergents, shampoos, cleaning agents
- Most synthetic; not always biodegradable (environmental issue)
11. Worked Examples
Example 1: Catenation
What is catenation? Give an example.
- Catenation = ability to form long chains/rings with same atom.
- Example: Carbon forms millions of compounds with C-C chains.
Example 2: Identify
Identify: CH₃-CH₂-OH
- Has 2 carbons, OH group → ethanol (ethyl alcohol)
Example 3: Saturated vs Unsaturated
Distinguish C₂H₆ and C₂H₄.
- C₂H₆ (ethane): saturated (only single bonds)
- C₂H₄ (ethene): unsaturated (has C=C double bond)
Example 4: Soap Working
Why doesn't soap clean in hard water?
- Hard water has Ca²⁺, Mg²⁺ ions.
- Soap reacts with these to form INSOLUBLE precipitates (scum).
- Less soap available for cleaning.
- Solution: use detergents (which don't form precipitates).
12. Common Mistakes
-
Carbon makes ionic bonds
- NO. Carbon forms COVALENT bonds (sharing electrons).
-
All hydrocarbons are alkanes
- WRONG. Three types: alkanes (single bonds), alkenes (double), alkynes (triple).
-
Methane is CH₂
- WRONG. Methane is CH₄ (carbon forms 4 bonds).
-
Soap = detergent
- DIFFERENT. Soap = sodium salt of fatty acid. Detergent = synthetic, works in hard water.
-
Ethanol is unsafe for drinking
- It IS in alcoholic drinks (regulated). But METHANOL is poisonous.
13. Indian Context
Indian Pharmaceutical Industry
- 'Pharmacy of the world'
- Major exports of generic drugs
- All based on carbon compound chemistry
Indian Petroleum
- Reliance, IOCL produce petrol, diesel (hydrocarbons)
- Major economy contributor
Indian Polymer Industry
- Plastics, fibres, rubbers — all carbon compounds
14. Conclusion
Carbon and its Compounds open the door to ORGANIC CHEMISTRY:
- Tetravalency + Catenation = millions of compounds
- Hydrocarbons (alkanes, alkenes, alkynes)
- Functional groups add diversity
- Ethanol, ethanoic acid are key compounds
- Soaps and detergents clean our world
This chapter is FOUNDATIONAL for Class 11-12 organic chemistry. Practice 15+ problems.
Carbon: the element of life and modern civilisation.
