1 Physical and chemical properties

Alkanes and cycloalkanes are saturated hydrocarbons Remember that the shape around the carbon atom in saturated hydrocarbons is tetrahedral and the bond angle is 109.5O The shape is tetrahedral as a result of the four bond pairs of electrons equally repelling. C C H H H H H H Boiling Point The increasing boiling points of the alkane homologous series can be explained by the increasing number of electrons in the bigger molecules causing an increase in the size of the induced dipole–dipole interactions (London forces) between molecules. The shape of the molecule can also have an effect on the size of the induced dipole–dipole interactions (London forces) . Long chain alkanes have a larger surface area of contact between molecules for London force to form than compared to spherical shaped branched alkanes and so have stronger induced dipole– dipole interactions and higher boiling points. One sp2 orbital from each carbon overlap to form a single C-C bond called a sigma σ bond C C sigma σ bond Formation of σ bond Rotation can occur around a sigma bond Reactivity The low reactivity of alkanes with many reagents can be explained by the high bond enthalpies of the C-C and C-H bonds and the very low polarity of the σ-bonds present.