Why are the halogens not found naturally in the earth's crust as the pure elements?

Answer 1

The halogens are not found naturally in the earth's crust as pure elements because of their extreme reactivity. Because the halogens are close to having completely filled electron shells, they will often react with other substances in order to gain an electron. As an especially noteworthy case, fluorine is the most reactive of the halogens (and elements in general), and will even react with glass. Therefore, the halogens are found naturally as compounds, not pure elements.

Answer 2

Halogens are highly reactive elements that readily combine with other elements to form compounds. This reactivity prevents halogens from being found in their pure elemental form in nature. Instead, halogens are commonly found in the Earth's crust combined with metals or other elements to form compounds such as salts.