Notes On Physical Properties - CBSE Class 12 Chemistry
Alkyl halides are colourless and may have a sweet smell. Many volatile alkyl halides have a sweet smell and it can be noticed when the concentration is relatively high. As the number of carbons increases for a series of alkyl halides, the boiling point increases. Boiling point increases as the halogen increases in size (from fluorine to iodine). Due to the greater polarity and higher molecular mass of haloalkanes as compared to the parent hydrocarbons, the dipole-dipole and Van der Waals forces of attraction are stronger in these compounds; the haloalkanes have higher boiling points than those of hydrocarbons of comparable molecular mass. The boiling points of isomeric haloalkanes decrease with an increase in branching. This is due to increase in branching, the molecule attains spherical shape with less surface area. This results in a decrease in the magnitude of Van der Waals forces, and hence the decrease in boiling point. Haloalkanes have very low solubility in water, but will dissolve in organic solvents. Alkyl fluorides and alkyl chlorides are less dense than water, but alkyl bromides and alkyl iodides are denser than water. Aryl halides are polar molecules due to the presence of the polar carbon-halogen bond, but they are less polar than alkyl halides. Aryl halides have physical properties very similar to alkyl halides. Aryl halides have insoluble in water and denser than water. Among dihalobenzenes para dihalobenzenes have higher melting points than their ortho and meta isomers.

Summary

Alkyl halides are colourless and may have a sweet smell. Many volatile alkyl halides have a sweet smell and it can be noticed when the concentration is relatively high. As the number of carbons increases for a series of alkyl halides, the boiling point increases. Boiling point increases as the halogen increases in size (from fluorine to iodine). Due to the greater polarity and higher molecular mass of haloalkanes as compared to the parent hydrocarbons, the dipole-dipole and Van der Waals forces of attraction are stronger in these compounds; the haloalkanes have higher boiling points than those of hydrocarbons of comparable molecular mass. The boiling points of isomeric haloalkanes decrease with an increase in branching. This is due to increase in branching, the molecule attains spherical shape with less surface area. This results in a decrease in the magnitude of Van der Waals forces, and hence the decrease in boiling point. Haloalkanes have very low solubility in water, but will dissolve in organic solvents. Alkyl fluorides and alkyl chlorides are less dense than water, but alkyl bromides and alkyl iodides are denser than water. Aryl halides are polar molecules due to the presence of the polar carbon-halogen bond, but they are less polar than alkyl halides. Aryl halides have physical properties very similar to alkyl halides. Aryl halides have insoluble in water and denser than water. Among dihalobenzenes para dihalobenzenes have higher melting points than their ortho and meta isomers.

Previous
Next