Carbon Bonding and Structure

Alkanes (Saturated Hydrocarbons)

Alkanes are the simplest hydrocarbons. They are described as "saturated" because their carbon atoms are joined only by single covalent bonds (C-C). The general formula for the alkanes is:

$$C_{n}H_{2n+2}$$

where $n$ represents the number of carbon atoms.

The names of alkanes use specific prefixes to indicate the number of carbons:

• Meth- (1 carbon)
• Eth- (2 carbons)
• Prop- (3 carbons)
• But- (4 carbons)
• Pent- (5 carbons)
• Hex- (6 carbons)

Alkanes can also exhibit isomerism, where molecules have the same molecular formula but different arrangements of atoms, leading to different physical properties. For example, butane and methylpropane are isomers.

Alkenes (Unsaturated Hydrocarbons)

Unlike alkanes, alkenes are "unsaturated" because they contain at least one carbon-carbon double bond (C=C). A double bond is a covalent bond resulting from the sharing of four electrons (two pairs) between two atoms. The general formula for alkenes is:

$$C_{n}H_{2n}$$

where $n \ge 2$. Because of this double bond, alkenes are significantly more reactive than alkanes.

From Molecules to Polymers

One of the most important applications of carbon bonding is polymerisation. A polymer is a substance made of many small, repeating units called monomers.

Addition Polymerisation

Addition polymers are specifically created from monomers that contain carbon-carbon double bonds, such as ethene or propene. During the reaction, the double bond "breaks open," allowing the carbon atoms to form new single bonds with adjacent monomer molecules.

For example, when ethene ($C_{2}H_{4}$) undergoes polymerisation, it forms poly(ethene).

Common addition polymers include:

• Poly(ethene): Used for plastic bags and bottles.
• Polyvinyl chloride (PVC): Used for construction pipes and waterproof clothing.
• Polystyrene: Used for disposable dinnerware and insulation.

Note on Properties: The physical properties of a plastic can be altered by changing the length of the polymer chain, how the chains are linked, or by adding other compounds.

Combustion of Hydrocarbons

Because hydrocarbons contain high amounts of chemical energy, they are widely used as fuels. When these fuels react with oxygen, they undergo combustion.

1. Complete Combustion: Occurs when there is a plentiful supply of oxygen. It produces carbon dioxide and water, releasing the maximum amount of energy.

   $$\text{hydrocarbon} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}$$

   Example (Propane):

   $$\begin{aligned} C_{3}H_{8} + 5O_{2} \rightarrow 3CO_{2} + 4H_{2}O \end{aligned}$$

2. Incomplete Combustion: Occurs when the oxygen supply is limited. This produces carbon monoxide (a toxic gas) and carbon (soot), and releases less energy than complete combustion.