Question

Chlorine, bromine and iodine are elements in Group VII of the Periodic Table.
Describe the trend in colour and physcial state at room temperature and pressure as the atomic number increases.

Answer 1

• Halogens display smooth variations in their physical properties. Fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. Their melting and boiling points steadily increase with atomic number.
• All halogens are coloured. This is due to absorption of radiations in visible region which results in the excitation of outer electrons to higher energy level.
  
• By absorbing different quanta of radiation, they display different colours. For example, $F_2,$ has yellow,$C{l}_2$ , greenish yellow, $B{r}_2$, red and $I_2, $violet colour.
• Fluorine and chlorine react with water. Bromine and iodine are only sparingly soluble in water but are soluble in various organic solvents such as chloroform, carbon tetrachloride, carbon disulphide and hydrocarbons to give coloured solutions.