9701 · 11.1
Physical properties of the Group 17 elements — FAQ
Frequently asked questions for 9701 Physical properties of the Group 17 elements. Direct answers first, then deeper explanation — then practise with marking.
Why isn't astatine (At) usually discussed in detail?
Astatine is highly radioactive and has no stable isotopes. Its most stable isotope has a half-life of only about 8 hours, which makes it extremely difficult and dangerous to study its physical properties in the quantities needed. Its properties are generally extrapolated from the trends of the other halogens.
Are halogens soluble in water?
As non-polar molecules, halogens have low solubility in a polar solvent like water. They are much more soluble in non-polar organic solvents, such as hexane or tetrachloromethane. Note that some halogens, like chlorine, do react with water to a limited extent.
If the F-F bond is so weak, why is fluorine the most reactive halogen?
Reactivity depends on both the energy needed to break bonds (activation energy) and the energy released when forming new bonds. While the F-F bond is weak and easy to break (low activation energy), fluorine is the most electronegative element and forms exceptionally strong bonds with other elements. The very large amount of energy released when these new, strong bonds are formed makes the overall reaction highly exothermic and thermodynamically favourable.