How does the molecular structure of alkanes affect their reactivity?

The molecular structure of alkanes, being saturated hydrocarbons with single bonds, makes them relatively unreactive.

Alkanes are a type of hydrocarbon, which means they are composed of hydrogen and carbon atoms. The molecular structure of alkanes is characterised by single covalent bonds between the carbon atoms and the hydrogen atoms. This type of bond is known as a sigma bond, which is very strong and stable. This stability is one of the main reasons why alkanes are relatively unreactive.

The carbon atoms in alkanes are sp3 hybridised, meaning they form four sigma bonds with other atoms. These bonds are arranged in a tetrahedral shape around the carbon atom, which further contributes to the stability of the molecule. The bond angles in alkanes are approximately 109.5 degrees, which is the most stable arrangement of bonds around a carbon atom. This stability reduces the reactivity of alkanes.

Furthermore, alkanes are non-polar molecules. This is because the electronegativity difference between carbon and hydrogen is very small, resulting in a negligible dipole moment. This lack of polarity means that alkanes do not readily react with polar substances, further reducing their reactivity.

However, alkanes can undergo certain types of reactions, such as combustion and substitution reactions. Combustion reactions occur when alkanes react with oxygen to produce carbon dioxide and water. This reaction is exothermic, releasing energy in the form of heat and light. Substitution reactions occur when a hydrogen atom in an alkane is replaced by another atom or group of atoms. This type of reaction typically requires the presence of a catalyst and heat to overcome the stability of the alkane molecule.

In summary, the molecular structure of alkanes, characterised by strong sigma bonds, tetrahedral bond angles, and non-polarity, makes them relatively unreactive. However, under certain conditions, they can undergo combustion and substitution reactions.