Carbon and its Compounds — Class 10 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 10 Science, Chemistry — Chapter 11. The chemistry of carbon — the element behind millions of organic compounds.
1. About this chapter
This chapter explains why carbon forms so many compounds, how organic compounds are classified and named (IUPAC), hydrocarbons, functional groups and homologous series, and important compounds like ethanol, ethanoic acid and soap.
2. Why carbon is versatile
- Tetravalency: carbon has 4 valence electrons and forms four covalent bonds.
- Catenation: carbon atoms link together in long chains, branches and rings.
- These two properties let carbon form millions of compounds.
3. Hydrocarbons and homologous series
- Hydrocarbons contain only carbon and hydrogen.
- Alkanes (saturated, single bonds): CₙH₂ₙ₊₂ — methane CH₄, ethane C₂H₆.
- Alkenes (one double bond): CₙH₂ₙ — ethene C₂H₄.
- Alkynes (one triple bond): CₙH₂ₙ₋₂ — ethyne C₂H₂.
- Homologous series: a family of compounds with the same functional group, successive members differing by –CH₂–, showing a gradual change in physical properties and similar chemical properties.
4. Functional groups and IUPAC names
| Functional group | Name | Example |
|---|---|---|
| –OH | alcohol | ethanol C₂H₅OH |
| –CHO | aldehyde | ethanal |
| >C=O | ketone | propanone |
| –COOH | carboxylic acid | ethanoic acid CH₃COOH |
- IUPAC nomenclature: root (number of C) + suffix (functional group), e.g. ethanol, ethanoic acid.
5. Important compounds
- Ethanol (C₂H₅OH): a liquid alcohol; used in beverages, as a solvent and fuel.
- Ethanoic acid (CH₃COOH): acetic acid; dilute solution = vinegar; a weak acid.
- Soaps: sodium/potassium salts of fatty acids, made by saponification (fat + NaOH). Soap cleans by forming micelles that trap oil/grease in hard-to-wash water it forms scum.
6. Worked examples
Example 1. Write the molecular formula of the alkane with 3 carbons. CₙH₂ₙ₊₂ → C₃H₈ (propane).
Example 2. Name the functional group in CH₃COOH and the compound. –COOH (carboxylic acid); the compound is ethanoic acid.
Example 3. What is saponification? The reaction of a fat/oil with alkali (NaOH) to form soap and glycerol.
7. Common mistakes
- Mistake: Writing the alkene/alkyne general formula wrongly. Fix: Alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂.
- Mistake: Confusing ethanol and ethanoic acid. Fix: Ethanol is the alcohol (–OH); ethanoic acid is the acid (–COOH, vinegar).
- Mistake: Thinking members of a homologous series have different functional groups. Fix: They share the same functional group and differ by –CH₂–.
8. Practice (book-back style)
- State two reasons why carbon forms a large number of compounds.
- Write the general formulae of alkanes, alkenes and alkynes.
- What is a homologous series?
- Name the functional groups in ethanol and ethanoic acid.
- Define saponification.
9. Answer key
- Tetravalency (forms 4 bonds) and catenation (self-linking of carbon atoms).
- Alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂.
- A family of compounds with the same functional group, successive members differing by –CH₂–.
- Ethanol: –OH (alcohol); ethanoic acid: –COOH (carboxylic acid).
- The reaction of a fat/oil with alkali to form soap and glycerol.
10. Quick revision
- Chemistry Ch 11 · carbon, hydrocarbons, functional groups, soap.
- Versatility: tetravalency + catenation.
- Alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂.
- Homologous series: same functional group, differ by –CH₂–.
- Ethanol (–OH), ethanoic acid (–COOH = vinegar); soap by saponification.
