How does reactivity change down Group VII?

Reactivity decreases down Group VII of the periodic table.

Group VII of the periodic table, also known as the Halogens, includes elements like Fluorine, Chlorine, Bromine, Iodine and Astatine. As you move down this group, the reactivity of these elements decreases. This is primarily due to the increase in atomic size and the increase in the number of electron shells.

Starting from the top, Fluorine is the most reactive element in Group VII. This is because it has the smallest atomic size and only two electron shells. Its small size allows it to attract electrons more effectively, making it highly reactive. As we move down the group, the atomic size increases and so does the number of electron shells. This increase in size and shells means that the outermost electrons are further away from the nucleus and are less strongly attracted to it.

For example, Chlorine, the next element down, is less reactive than Fluorine. It has three electron shells and a larger atomic size, which means its outermost electrons are less strongly attracted to the nucleus. This pattern continues with Bromine, Iodine and Astatine, each being less reactive than the one above it.

Another factor contributing to the decrease in reactivity is the increase in shielding effect. As the number of electron shells increases, the inner shells 'shield' the outermost electrons from the positive charge of the nucleus. This shielding effect reduces the pull of the nucleus on the outermost electrons, making it harder for the atom to gain an electron and thus reducing its reactivity.

In summary, the reactivity of elements in Group VII decreases as you move down the group due to an increase in atomic size, an increase in the number of electron shells and an increase in the shielding effect.