This lesson is an introduction to organic chemistry, the chemistry of carbon compounds. It focuses on the simplest organic compounds, hydrocarbons, which are essential as fuels and the building blocks for plastics.

1. What are Hydrocarbons?

• Definition: Organic compounds that contain only carbon (C) and hydrogen (H) atoms.

• Key Source: Crude oil (petroleum) is the main source of hydrocarbons. Fuels like petrol, diesel, kerosene, and LP gas are all mixtures of hydrocarbons.

2. Alkanes: The Saturated Hydrocarbons

• Definition: Alkanes are a family of hydrocarbons where the carbon atoms are joined together by single covalent bonds only. Because they have the maximum possible number of hydrogen atoms, they are called saturated hydrocarbons.

• General Formula: You must memorize this! The formula for any alkane is CnH2n+2, where 'n' is the number of carbon atoms.

• Naming: The first few alkanes have names you should know:

  • n=1: Methane

  • n=2: Ethane

  • n=3: Propane

  • n=4: Butane

  • n=5: Pentane (Mnemonic for the first four: Monkeys Eat Peeled Bananas)

Drawing Alkanes (First 5 Members)

You need to be able to draw the simple "straight-chain" structures for these. Remember that every carbon atom must form four bonds.

3. Ethene and Its Derivatives

• Ethene (An Alkene): Ethene (C₂H₄) is the simplest member of the alkenes. Alkenes are unsaturated hydrocarbons because they contain at least one carbon-carbon double bond (C=C).

  • Structure of Ethene: H H<br> \ /<br> C=C<br> / \<br> H H

• Derivatives of Ethene: These are molecules where one or more hydrogen atoms in ethene have been replaced by other atoms. They are important because they are the monomers for making famous plastics.

  • Chloroethene (Vinyl Chloride): One hydrogen is replaced by a chlorine (Cl) atom. Used to make PVC.

  • Tetrafluoroethene: All four hydrogens are replaced by fluorine (F) atoms. Used to make Teflon.

Exam Tips & Tricks

1. Saturated vs. Unsaturated: This is a key distinction. Alkanes = single bonds = saturated. Alkenes = double bonds = unsaturated.

2. General Formula is Gold: The formula CnH2n+2 for alkanes is frequently tested. Be ready to use it to find the molecular formula for a given number of carbon atoms.

3. Drawing Structures: Practice drawing the simple alkanes. The main rule is to make sure every carbon atom has exactly four lines (bonds) coming from it.

Know Your Monomers: For the next lesson on polymers, remember that ethene is the monomer for polythene, and chloroethene is the monomer for PVC. The names give you a clue!