How does reactivity change down Group I?

Reactivity increases down Group I of the Periodic Table as the atoms get larger and the outer electrons are less tightly held.

In Group I of the Periodic Table, also known as the Alkali Metals, the elements include Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr). As you move down the group, the reactivity of these elements increases. This is due to the increasing atomic size and the decreasing ionisation energy.

The atomic size increases down the group because each element has an extra electron shell compared to the one above it. This means the outermost electron is further away from the nucleus, which contains the protons that attract the electrons. As a result, the attraction between the nucleus and the outermost electron decreases, making it easier for the atom to lose this electron and form a positive ion. This is why alkali metals are so reactive: they readily lose their outer electron to achieve a stable electron configuration.

The ionisation energy, which is the energy required to remove an electron from an atom, also decreases down the group. This is because the outermost electron is less tightly held by the nucleus due to the increased distance and shielding effect of the inner shells. Therefore, less energy is needed to remove the outermost electron, making the atom more reactive.

In summary, the reactivity of Group I elements increases down the group due to the increasing atomic size and decreasing ionisation energy. This results in the outermost electron being less tightly held by the nucleus, making it easier for the atom to lose this electron and react with other substances.