Why are halogens highly reactive?

Halogens are highly reactive because they have seven electrons in their outermost shell and need one more to achieve stability.

Halogens, which include fluorine, chlorine, bromine, iodine, and astatine, are found in Group 7 of the Periodic Table. They are known for their high reactivity, which is primarily due to their electronic configuration. Each halogen atom has seven electrons in its outermost shell, just one short of the stable, full shell configuration of eight electrons. This makes them very eager to gain an extra electron to achieve this stability.

The desire to gain an electron and achieve a stable electronic configuration is what drives chemical reactions. In the case of halogens, this desire is particularly strong because they are so close to achieving a full outer shell. This makes them highly reactive, especially with elements that have one electron in their outermost shell, such as the alkali metals in Group 1 of the Periodic Table.

The reactivity of halogens decreases down the group. This is because as you go down the group, the outermost electrons are further from the nucleus and are less strongly attracted to it. This means that it is less easy for the atom to gain an extra electron, and so the reactivity decreases.

In summary, the high reactivity of halogens is due to their electronic configuration. They have seven electrons in their outermost shell and are very keen to gain an extra one to achieve a stable, full shell configuration. This drive to gain an electron is what makes them so reactive.