Quick Summary
Carbon forms a very large number of compounds because it has tetravalency and catenation. This chapter is important for covalent bonds, hydrocarbons, functional groups, ethanol, ethanoic acid, soaps, and detergents.
Key Definitions
- Tetravalency: Carbon has valency four and can form four covalent bonds.
- Catenation: Ability of carbon to form bonds with other carbon atoms.
- Covalent bond: Bond formed by sharing of electrons.
- Hydrocarbons: Compounds containing only carbon and hydrogen.
- Saturated hydrocarbons: Hydrocarbons with only single bonds.
- Unsaturated hydrocarbons: Hydrocarbons with double or triple bonds.
- Functional group: Atom or group of atoms that gives characteristic properties to an organic compound.
Why Carbon Is Special
Carbon has four valence electrons. It neither easily loses nor gains four electrons. Instead, it shares electrons and forms covalent bonds. Carbon-carbon bonds are strong, so carbon can form chains, branched structures, and rings.
Hydrocarbons
| Type | Bond | Example pattern |
|---|---|---|
| Alkane | Single bond | C-C |
| Alkene | Double bond | C=C |
| Alkyne | Triple bond | C#C |
Functional Groups
| Functional group | Family |
|---|---|
-OH | Alcohol |
-CHO | Aldehyde |
-COOH | Carboxylic acid |
-Cl, -Br | Halo compound |
Ethanol and Ethanoic Acid
Ethanol
- Belongs to the alcohol family.
- Used as a solvent and in some fuels.
- Burns to produce carbon dioxide and water.
Ethanoic Acid
- Belongs to the carboxylic acid family.
- Dilute ethanoic acid is present in vinegar.
- Reacts with bases to form salts and water.
Soaps and Detergents
Soaps and detergents help remove oily dirt from clothes and skin. Soap molecules have a water-loving part and an oil-loving part, so they can pull oil into water during washing.
Homologous Series and Naming
A homologous series is a family of compounds with the same functional group, differing by a –CH₂– unit; consecutive members differ by 14 u in molar mass and have similar chemical properties.
Important Reactions (worked)
Ethanol → Ethanoic acid (oxidation)
Esterification
Combustion of ethanol
Ethanoic acid + base / carbonate
Cleansing Action of Soap — in depth
A soap molecule has a long hydrophobic (oil-loving) hydrocarbon tail and a hydrophilic (water-loving) ionic head. In water, tails point inward toward the oil/dirt and heads point outward into the water, forming a micelle that lifts the dirt off and keeps it suspended so it rinses away.
Soaps fail in hard water (Ca²⁺/Mg²⁺ ions) because they form an insoluble scum. Detergents work even in hard water.
Textbook Solution Strategy
1. Identify whether the compound is saturated or unsaturated. 2. Look for the functional group. 3. Connect the functional group to the compound family. 4. Use tetravalency to check carbon bonding. 5. For soap questions, explain both water-loving and oil-loving parts.
Important Questions
One Mark
- What is catenation?
- Define hydrocarbon.
- Write the functional group of alcohol.
Two Marks
- Why does carbon form covalent compounds?
- Differentiate between saturated and unsaturated hydrocarbons.
- What is a functional group?
Five Marks
- Explain tetravalency and catenation of carbon.
- Describe ethanol and ethanoic acid with important properties.
- Explain the cleansing action of soap.
Common Mistakes
- Forgetting that carbon has valency four.
- Confusing alkane, alkene, and alkyne bonds.
- Writing functional groups without the correct symbol.
- Explaining soap action without mentioning oil-loving and water-loving parts.
Revision Checklist
- Tetravalency and catenation revised
- Alkane, alkene, and alkyne differences memorised
- Functional groups practised
- Ethanol and ethanoic acid properties revised
- Soap cleansing action explained once in writing