91Ó°ÊÓ

Halogens are generally found in compounds in their -1 oxidation state.They form ionic compounds with metals due to the large difference in their electronegativity.

They belong to the seventeenth group in the periodic table.

Due to the ionic nature, these compounds exist as ions in solution and can undergo displacement reactions. In displacement reactions, a more reactive element displaces a less reactive element from the solution.

Down the group, the reactivity of halogens decreases due to the increase in size. As the size increases, the nuclear charge on the valence electron decreases, reducing the element's electron affinity.

Therefore, a halogen higher in the group will be more reactive, and a halogen can displace another halogen below it in the periodic table. Halogens other than fluorine can exist in positive oxidation states and undergo disproportionation reactions.

(a) Rubidium is a metal with high electropositivity. It can react with bromine to form rubidium bromide, an ionic compound. The electronegativity difference between the ions is very high.

The balanced equation for the reaction is

$2Rb\left(s\right)+B{r}_2\left(l\right)→2RbBr\left(s\right)$

(b) Iodine undergoes disproportionation in solution to iodide and iodate ions. The oxidation state of iodine changes from 0 in iodine to -1 in iodide ion and +5 in iodate ion.

The balanced equation for the reaction can be given as

$3I_2\left(s\right)+3H_{2}O\left(l\right)→5HI\left(aq\right)+HI{O}_3\left(aq\right)$

(c) Bromine lies above iodine in the periodic table, and therefore, bromine is more reactive. When bromine is introduced into an iodide solution, bromine can displace iodide ions from the solution and form bromide. Solid iodine is formed in the solution.

The balanced equation for the reaction is

$B{r}_2\left(l\right)+2I^{-}\left(aq\right)→I_2\left(s\right)+B{r}^{-}\left(aq\right)$

(d) When calcium fluoride is mixed with concentrated sulfuric acid, a double displacement reaction occurs, and the fluoride ions and sulfate ions are exchanged between the metal ions.

The reaction is confirmed by calcium sulfate, which forms a precipitate in the solution. The balanced equation for the reaction is

$Ca{F}_2\left(s\right)+H_{2}S{O}_4\left(l\right)→2HF\left(g\right)+CaS{O}_4\left(s\right)$