Alkanes: Structure, Properties and Reactions

Ever wondered why petrol burns so well but doesn't dissolve in water? It's all about alkane structure and bonding. Alkanes contain only single covalent bonds (called sigma bonds), which form when atomic orbitals overlap directly between atoms.

These sigma bonds are incredibly strong because there's high electron density between the bonded nuclei, creating powerful electrostatic attraction. The atoms arrange themselves in a tetrahedral shape with bond angles of 109.5° around each carbon atom. This makes alkanes quite unreactive since the bonds are difficult to break and non-polar.

Boiling points increase as chain length grows because stronger intermolecular forces (IDD forces) develop between longer molecules. Branched alkanes have lower boiling points than straight-chain ones since they have fewer contact points for intermolecular forces to act.

Alkanes make excellent fuels through combustion reactions with oxygen. Complete combustion produces CO₂ and H₂O, whilst incomplete combustion (limited oxygen) creates dangerous carbon monoxide and soot. Smaller alkanes burn more easily because they're more volatile.

Key Point: Alkanes undergo free radical substitution with halogens under UV light or high temperatures (300°C), replacing hydrogen atoms with halogen atoms through initiation, propagation, and termination steps.