The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compounds derived from alkanes containing one or more halogens.
The boiling points of the halogenoalkanes depend on the strength of their intermolecular forces. As you go down group 7 from fluorine to iodine, the atomic radius of the halogen atoms, and the number of electron shells that they have, increases.This increases the instantaneous dipole –induced dipolebonds.This means the forces between the molecules are stronger which means more energy is needed to overcome them. The bigger the halogen atom and the more halogen atomsthere are, the higher the boiling point.
Reactivity of the Halogenoalkanes
Halogenoalkanes contain a polar carbon-halogen bond.The polarity arises from the different electronegativities of the carbon and halogen atoms.Halogenatoms are more electronegative than carbon atoms.The bonded electron pair is attracted more towards the halogen atom than towards the carbon atom.The result is a polar bond.This illustrates the polarity in a molecule of bromomethane.
The electronegativity decreases down the group, resulting in a decrease in polarity of the carbon-halogen bond from fluorine to iodine.The carbon-halogen bond becomes weaker as the size of the halogen atom increases.This makes the bond easier to break and the compounds become more reactive.
Fluro-compounds are very unreactive.
Chloro-compounds are reasonably stable in the troposphere and can react to produce chlorine radicals that deplete ozone.
Bromo-and iodo-compounds are reactive and so are useful as intermediates in chemical synthesis.
Drafted by Eunice (Chemistry)