Alkanes | Chemistry for Grade 11 (IGCSE) PDF Download

Alkanes: Properties & Bonding

• Alkanes belong to a category of hydrocarbons characterized by having only single carbon-carbon bonds, making them saturated compounds devoid of double bonds.
• Their general formula is C_nH_2n+2, with physical properties gradually changing as the carbon atom count in the chain increases.
• Despite being generally unreactive, alkanes can undergo combustion reactions, be subjected to cracking processes yielding smaller molecules, and participate in substitution reactions with halogens under light exposure.
• Methane, a prime example of an alkane, constitutes a significant portion of natural gas and, upon complete combustion, produces carbon dioxide and water according to the equation: CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l).

Substitution Reaction of Alkanes with Halogens

• Substitution reactions involve the exchange of one atom or group of atoms with another in a compound.
• Alkanes participate in substitution reactions with halogens when exposed to ultraviolet radiation, a process known as photochemical reaction.
• Ultraviolet light serves as the activation energy (E_a) required for the reaction to proceed.
• In this reaction, a hydrogen atom in the alkane is replaced by a halogen atom.
• The extent of substitution can vary depending on the intensity of ultraviolet radiation present.