16.1    Introduction to Halogenoalkaes

What are halogenoalkanes?

• Halogenoalkanes(or alkyl halides) are compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine, bromine or iodine).
• Halogenoalkanes can be classified as primary, secondary or tertiary depending on the number of alkyl groups(R groups) attached to the carbon atom holding the halogen atom

• Some examples of halogenoalkanes:

Physical properties of halogenoalkanes

• i) Boiling point of the halogenoalkanes increases as the molecular size increases. This is because there are more electrons in larger molecules and more  temporary dipoles can be set up, resulting in stronger van der Waal’s forces.ii)Primary halogenoalkanes have higher boiling point compared to secondary and tertiary halogenoalkanes of the same molecular weight. This is because the surface area of primary halogenoalkanes is higher, more    temporary dipoles can be set up, resulting in stronger van der Waal’s forces

• 1. Halogenoalkanes are insoluble in water but soluble in organic solvents.
  2. This is because when dissolved in water(polar solvents), the energy needed to break the hydrogen bonds between water molecules is too high. The energy released when halogenoalkane-water attraction is set up is not enough to compensate it. This makes the structure to gain energy overall, making it less stable.
  3. While when it is dissolved in organic solvents, the halogenoalkane-solvent attraction is strong enough to compensate the energy needed to break the weak van der Waal’s forces between organic molecules