Class 12 Chemistry Haloalkanes and Haloarenes Physical Properties of halo alkanes

Physical Properties of halo alkanes

  • Alkyl halides are colorless in pure state. Bromides and iodides cultivate colour on exposure to light
  • Volatile halogen compounds possess a sweet smell.
  • Intermolecular forces of attraction of halogen derivatives are stronger due to greater polarity and molecular mass as well compared to the parent hydrocarbon thereby resulting in higher boiling points of chlorides, bromides and iodides compared to hydrocarbons of equivalent molecular mass.
  • The boiling points of alkyl halides for same alkyl group follow the order: RI> RBr> RCl> RF due to the increase in size and mass of halogen atom thereby increasing the extent of van der Waal forces.

 

  • In isomeric haloalkanes the boiling points decreases with increase in branching.

 

  • Para-isomers possess high melting point compared to ortho and meta-isomers due to the symmetry of para-isomers fitting in crystal lattice better than ortho- and meta-isomers.
  • Density increases with increase in number of carbon atoms, halogen atoms and atomic mass of the halogen atoms. Consequently the density of Bromo, iodo and polychloro derivatives of hydrocarbons is greater than water.
  • The haloalkanes are only very slightly soluble in water due to release of less energy during the setup of new attractions between the haloalkane and the water molecules which in turn is insufficient to overcome the attractions between the haloalkane molecules and break the hydrogen bonds between water molecules.
  • Haloalkanes dissolves easily in organic solvents due to the new intermolecular forces of attractions between haloalkanes and solvent molecules having equivalent strength as the one that is broken in separate haloalkane and solvent molecules.

 

Problem:

Arrange each set of compounds in order of increasing boiling points.

(i) Bromomethane, Bromoform, Chloromethane, Dibromomethane.

(ii) 1-Chloropropane, Isopropyl chloride, 1-Chlorobutane.

Solution:

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