A quick revision summary for right before the exam: every definition, equation and named fact from the chapter, all in one place. The full notes are available separately for detailed reading.
1 Covalent Bonding and Allotropes
- Covalent bond: formed by sharing a pair of electrons between two atoms, so both get a full outer shell
- H₂: single bond · O₂: double bond · N₂: triple bond · CH₄: carbon (tetravalent) shares with 4 H atoms
- Carbon does not readily form C⁴⁺ or C⁴⁻ ions: both need too much energy or leave an unstable ion
- Diamond: 4 bonds/carbon, rigid 3-D network, hardest substance known, does not conduct
- Graphite: 3 bonds/carbon (one is a double bond, so valency is satisfied), hexagonal layers, soft and slippery, conducts electricity
- Fullerene: C-60, football-shaped, named after architect Buckminster Fuller
2 Why Carbon Forms So Many Compounds
Carbon’s unique ability to bond with other carbon atoms, forming chains, branches or rings. Silicon manages only 7-8 atoms; carbon’s chains are far longer and stable.
Carbon’s valency of 4: it bonds to 4 other atoms (carbon or another element). Small size lets carbon’s nucleus hold shared electrons strongly, giving strong bonds.
1828: Friedrich Wöhler prepared urea from ammonium cyanate, disproving the “vital force” theory that carbon compounds needed a living system to form.
3 Classifying Carbon Compounds
| C atoms | Name | Formula |
|---|---|---|
| 1 | Methane | CH₄ |
| 2 | Ethane | C₂H₆ |
| 3 | Propane | C₃H₈ |
| 4 | Butane | C₄H₁₀ |
| 5 | Pentane | C₅H₁₂ |
| 6 | Hexane | C₆H₁₄ |
Saturated: only single C-C bonds (alkanes), less reactive. Unsaturated: a double (alkenes) or triple (alkynes) C-C bond, more reactive.
Same molecular formula, different structure, e.g. butane’s straight-chain and branched forms.
Functional groups: -Cl/-Br haloalkane · -OH alcohol · -CHO aldehyde · -CO- ketone · -COOH carboxylic acid.
Homologous series: same functional group, successive members differ by -CH₂- (14 u). Alkene formula: .
Naming: count carbons → base name; add prefix/suffix for the functional group; drop final “e” before a vowel suffix (propan + one = propanone); unsaturation changes “ane” to “ene”/”yne”.
4 Reactions of Carbon Compounds
(substitution)
- Combustion: saturated → clean flame; unsaturated/limited air → yellow, sooty flame; coal/petroleum’s N and S give polluting oxides
- Oxidation: alkaline KMnO₄ or acidified K₂Cr₂O₇ (oxidising agents) turn alcohols into acids
- Addition: unsaturated + H₂, with Pd/Ni catalyst → saturated (e.g. hydrogenating vegetable oil)
- Substitution: chlorine replaces hydrogen one by one, in sunlight
5 Ethanol and Ethanoic Acid
| Ethanol | Ethanoic acid | |
|---|---|---|
| Litmus | Neutral | Turns blue red |
| MP / BP | 156 K / 351 K | 290 K (glacial acetic acid) |
| With Na | H₂ gas + sodium ethoxide | H₂ gas + sodium ethanoate |
| With NaHCO₃ | No reaction | Brisk fizz, CO₂ gas |
(dehydration)
(esterification)
(saponification)
Vinegar: 5-8% ethanoic acid in water. Methanol: oxidised to methanal in the liver; can cause blindness or death. Denatured alcohol: ethanol + methanol (poison) + blue dye.
6 Soaps and Detergents
A cluster of soap molecules in water, hydrophobic (hydrocarbon) tails pointing into an oil droplet, hydrophilic (ionic) heads facing outward into the water.
- Soap = sodium/potassium salt of a long-chain carboxylic acid
- Hard water (Ca²⁺/Mg²⁺) + soap → insoluble curdy scum, poor lather
- Detergents (sulphonate/ammonium salts) do not form this precipitate → work well in hard water
- Micelles stay suspended as a colloid (ion-ion repulsion) and scatter light, so soap solution looks cloudy
- Covalent bond = shared electron pair. Diamond: 4 bonds/C, hard, insulator. Graphite: 3 bonds/C, soft, conducts. Fullerene: C-60, football shape
- Catenation + tetravalency = millions of carbon compounds
- Saturated (alkanes, single bonds) vs unsaturated (alkenes double, alkynes triple)
- Homologous series: same functional group, +14 u per member
- Ethanol: neutral, reacts with Na, dehydrates to ethene at 443 K
- Ethanoic acid: weak acid, vinegar, glacial (290 K), reacts with base and carbonates giving CO₂
- Soap cleans via micelles; fails in hard water (scum); detergents don’t