Alkanes, being saturated hydrocarbons, possess only single bonds between carbon atoms. These single bonds, or sigma (σ) bonds, are quite strong and involve head-on overlap of orbitals, leading to greater stability. In contrast, alkenes have a double bond which consists of a sigma (σ) bond and a pi (π) bond. The pi bond is weaker as it's formed by the sideways overlap of p-orbitals. This makes alkenes more reactive and predisposed to addition reactions where the π bond is broken. Alkanes, lacking this π bond and being shielded by the robust σ bonds, primarily undergo substitution reactions when reactive species like radicals are involved.

Ultraviolet (UV) light plays a critical role in the homolytic fission of chlorine molecules, resulting in the formation of two chlorine radicals. When chlorine is exposed to UV light, the energy from the light is absorbed by the chlorine molecule. This energy is sufficient to break the Cl-Cl bond, causing the molecule to split homolytically, where each chlorine atom takes away one electron, forming two chlorine radicals. This initiation step is crucial because these radicals can then go on to react with alkanes, triggering a series of chain reactions.

Alkanes are non-polar due to the near identical electronegativities of carbon and hydrogen atoms, leading to a lack of significant charge separation within the molecule. Water, on the other hand, is a highly polar molecule. The principle "like dissolves like" in chemistry implies that polar solvents, like water, tend to dissolve polar solutes, while non-polar solvents dissolve non-polar solutes. Given this, the non-polar nature of alkanes means that they are virtually insoluble in water. Instead, alkanes will tend to separate from water, forming a distinct layer, which is a characteristic often observed in oil spills in aquatic environments.

Radicals demonstrate a unique selectivity towards hydrogens based on their positioning in a hydrocarbon molecule. This phenomenon is termed 'regioselectivity'. The reason lies in the stability of the radicals that are formed post the hydrogen abstraction. For instance, a tertiary radical (one formed on a tertiary carbon) is more stable than a secondary radical, which in turn is more stable than a primary radical. This is due to the dispersal of the unpaired electron over a larger volume and the hyperconjugation effect. As a result, when a radical reacts with a hydrocarbon having different types of hydrogens, it prefers to abstract a hydrogen such that the most stable radical is formed.

Hyperconjugation is a stabilising interaction that involves the overlap of an adjacent sigma bond's orbital with the orbital of a radical or a positively charged centre. In the context of alkanes, when a radical is formed on a carbon, adjacent C-H sigma bonds can engage in hyperconjugation. This phenomenon disperses the electron deficiency of the radical over multiple atoms, increasing the stability of the radical. For instance, tertiary radicals are more stable than secondary radicals, which are more stable than primary radicals. This is because tertiary radicals have more neighbouring hydrogen atoms available for hyperconjugative interactions, thereby offering greater stability.