Alkanes and Alkenes

Alkanes and Alkenes

Understanding Alkanes

• Alkanes are a class of hydrocarbons, compounds consisting of only hydrogen and carbon atoms.
• They are characterised by single covalent bonds between carbon atoms and are therefore termed as saturated hydrocarbons.
• The simplest alkane is methane (CH4), followed by ethane (C2H6), propane (C2H8), and so on.
• The general formula for alkanes is CnH2n+2, where n represents the number of carbon atoms.

Properties of Alkanes

• Alkanes are generally non-polar molecules, meaning they are mostly insoluble in water but soluble in organic solvents.
• They have low reactivity because the carbon-carbon and carbon-hydrogen bonds in alkanes are relatively stable.

Combustion of Alkanes

• Alkanes are important as fuels. When burnt in oxygen, they undergo complete combustion to form carbon dioxide and water.
• However, with a limited oxygen supply, alkanes undergo incomplete combustion, resulting in poisonous carbon monoxide, or even producing soot (carbon).

Understanding Alkenes

• Alkenes are also hydrocarbons, but unlike Alkanes, they contain at least one carbon-carbon double bond. This makes them unsaturated hydrocarbons.
• The simplest alkene is ethene (C2H4), followed by propene (C3H6), and so on.
• The general formula for alkenes is CnH2n.

Properties of Alkenes

• Alkenes are more reactive than alkanes due to the presence of a double bond which can easily break and form new bonds.
• Like alkanes, alkenes are also non-polar and insoluble in water, but soluble in organic solvents.

Reactions of Alkenes

• Alkenes can participate in addition reactions, where the carbon-carbon double bond breaks to allow other atoms or molecules to add to the carbons.
• For instance, alkenes react with bromine water (a test for unsaturation) to produce a colourless dibromo compound.
• Alkenes also burn in air, but combustion is usually less clean than for alkanes, giving sooty flames.