Organic Chemistry
Compound Names
Organic chemistry deals with 3 types of organic (carbon-containing) molecules in IGCSE:
- Alkenes
- Alkanes
- Alcohols
All 3 groups of molecules contain carbon and hydrogen atoms. However, their structures are slightly different. Each molecule from these groups is named using a prefix that denotes the number of carbon atoms and a suffix that identifies the homologous series.
- Alkene: ene
- Alkane: ane
- Alcohol: anol
Only the names of the first 4 molecules of each group need to be known for IGCSE.
| Carbon Atoms | Alkenes | Alkanes | Alcohols |
|---|---|---|---|
| 1 | ? | Methane | Methanol |
| 2 | Ethene | Ethane | Ethanol |
| 3 | Propene | Propane | Propanol |
| 4 | Butene | Butane | Butanol |
Methene does not exist because it is impossible for a single carbon atom to form double bonds with itself.
Homologous Series
Homologous series are a family of compounds with the same general formula and similar chemical properties. Compounds in the same homologous series have the:
- same functional group
- same general formula
- similar chemical reactions
- similar physical properties
| Series | General Formula | Saturated |
|---|---|---|
| Alkenes | CnH2n | close |
| Alkanes | CnH2n+2 | check |
| Alcohols | CnH2n+1OH | check |
Alkenes have double bonds because they are unsaturated (some carbon atoms need more bonds). Alkanes are saturated with hydrogen atoms. Alcohols have a hydroxide molecule attached to them which means they are not hydrocarbons.
Alkenes
An alkene is an unsaturated hydrocarbon that contains 1 (carbon) double covalent bond.
Cracking
Cracking is the process of breaking down larger alkane molecules into smaller alkenes and alkanes. Sometimes, hydrogen can be produced in the process as well.
Alkanes
An alkane is a saturated hydrocarbon that only contains single covalent bonds. Alkanes are less reactive than alkenes.
Fuels
Fractional Distillation of Petroleum
Petroleum is a mixture of hydrocarbons with different boiling points. These hydrocarbons can be separated into fractions in a furnace.
The temperature is not the same throughout the furnace.
- Bottom of the furnace is hot so only the fraction with the highest boiling point (bitumen) can condense
- Top of the furnace is cool so only the fraction with the lowest boiling point (refinery gas) can remain as vapour
The different fractions have different uses.
- Refinery Gas: bottled gas for heating
- Gasoline: fuel in cars
- Naphtha: feedstock for manufacturing chemicals
- Diesel: fuel in diesel engines
- Bitumen: road surfaces
Fractions of petroleum are separated according to their boiling points.
- Petroleum is heated and vapour rises
- Vapour cools down as it rises through the furnace
- Fractions condense when the vapour reaches their boiling points
Polymer
A polymer is a long chain molecule formed from small repeating units called monomers.
Addition Polymerisation
The addition of multiple monomer units results in an addition polymer. Addition polymers have the poly prefix attached to the name of the monomer. For example, poly(ethene) is an addition polymer made from multiple ethene molecules.
The orientation of each monomer does not matter as long as they have the same chemical structure and formula.
Condensation Polymerisation
Nylon is an example of a condensation polymer. Condensation polymerisation forms a polymer and a small molecular waste product while addition polymerisation only produces a polymer.
Nylon is made from a dicarboxylic acid and a diamine.
- dicarboxylic acid loses its hydroxide
- diamine loses one of its hydrogens
- hydrogen and hydroxide react to produce water
- dicarboxylic acid and diamine join together to form a larger molecule