Q. What are the Chemical Properties of Halogens?
Ans.
he halogens have 7 valence electrons in their outermost shell. Note that 7 is one electron short of the octet. Hence, they show a strong tendency to accept an electron to form an X- ion. The X- ion has a stable noble gas configuration and has a -1 charge. The following illustration shows the reaction whereby a chlorine atom accepts an electron and becomes a negatively charged chlorine ion.
The halogens form covalent compounds with many non-metal elements. Since the halogens are among the most electronegative elements, an increase in the oxidation number of the other element usually results. The halogens are thus oxidizing agents.
For example, consider the reaction of:
C + 2Cl2 -> CCl4
The chlorine oxidizes the carbon from an oxidation number of 0 to a +4 oxidation number. In doing so, the chlorine itself becomes reduced. It's oxidation number decreases from 0 to -1.
As the attraction of the nucleus for electrons in the outermost shell decreases down the family, the size of the halogen atoms increases. Hence, the oxidizing strength and reactivity of the halogens decrease down the group.
Fluorine is the first element in the group. Fluorine is an exceptionally strong oxidizing agent and is extremely reactive.
Fluorine reacts vigorously with cold water to form hydrogen fluoride and oxygen:
2F2 + 2H2O -> 4HF + O2
Chlorine is a very reactive element and a powerful oxidizing agent.
Chlorine reacts less readily with water and forms hydrogen ions, chloride ions, and hypochlorous acid. Hypochlorous acid (HOCl) is a weak acid.
2Cl2 + 2H2O -> H+ + Cl- + HOCl
Bromine and iodine are chemically very similar to chlorine, but reactivity and oxidizing strength decrease down the group.
Bromine is less soluble in water than chlorine. Saturated solutions of chlorine and bromine - known as chlorine water and bromine water - are convenient sources of these elements.
Iodine is not very soluble in water. Iodine dissolves better in other solvents. The color of an iodine solution depends upon the solvent. With solvents containing oxygen (for example,ethers and alcohols) the solution is brown.