Nature's chemistry
Hydrocarbons and homologous series
A homologous series is a family of hydrocarbons with similar chemical properties who share the same general formula.
We will look at three hydrocarbon series: alkanes, alkenes and the cycloalkanes. Hydrocarbons are compounds that contain only hydrogen and carbon.
Alkanes
The first homologous series is the alkanes. Their names all end in –ane.
The alkanes have many uses:
- methane – (natural gas) cooking, heating
- propane – used in gas cylinders for BBQ etc
- octane – used in petrol for cars
The general formula of the alkanes is \({C_n}{H_{2n + 2}}\). They are insoluble in water.
The names, molecular formula and the structural formula of the first eight alkanes must be learned. Using a mnemonic can make learning the names easier.
| Methane | CH4 | Monsters |
| Ethane | C2H6 | Eat |
| Propane | C3H8 | Pupils |
| Butane | C4H10 | But |
| Pentane | C5H12 | Prefer |
| Hexane | C6H14 | Hairy |
| Heptane | C7H16 | Haggis |
| Octane | C8H18 | Occasionally |
| Methane |
|---|
| CH4 |
| Monsters |
| Ethane |
|---|
| C2H6 |
| Eat |
| Propane |
|---|
| C3H8 |
| Pupils |
| Butane |
|---|
| C4H10 |
| But |
| Pentane |
|---|
| C5H12 |
| Prefer |
| Hexane |
|---|
| C6H14 |
| Hairy |
| Heptane |
|---|
| C7H16 |
| Haggis |
| Octane |
|---|
| C8H18 |
| Occasionally |
General formula, functional group and properties of alkanes.
