Question

Discuss the following property and its variation with reference to the elements of group 17:

Reactivity

Answer 1

1. Group 17 elements (F, Cl, Br, I, At) are called halogens and are very reactive non-metals.
2. Reactivity arises because halogens have 7 electrons in the outer shell, needing one more to attain noble gas configuration.
3. Halogen molecules (X₂) have low bond dissociation energy, making it easy to break bonds and react.
4. They have high negative electron gain enthalpy, showing a tendency to gain electrons and form halide ions (X⁻).
5. Reactivity decreases down the group from fluorine (most reactive) to iodine due to increasing atomic size and decreasing electronegativity.
6. Fluorine can displace all other halogens from their salts; chlorine displaces bromine and iodine; bromine displaces iodine.
7. The reactivity trend is F > Cl > Br > I. This makes fluorine the strongest oxidising agent among halogens.