Chemistry – The Periodic Table - Arrangement of elements | e-Consult

The reactivity of these metals increases as you move down a group. Therefore, reactivity increases from Aluminium to Magnesium to Sodium. This is because reactivity increases as the outermost electron is further from the nucleus and therefore less tightly held. Sodium (Na) has an electronic configuration of 2, 8, 1. It readily loses this single electron to form a positive ion (Na+), making it highly reactive. Magnesium (Mg) has an electronic configuration of 2, 8, 2. It has two valence electrons, which are held more tightly than a single electron, so it is less reactive than Sodium. Aluminium (Al) has an electronic configuration of 2, 8, 3. It has three valence electrons, which are held even more tightly than two, making it the least reactive of the three. The larger atomic radius of the metals as you go down the group also contributes to lower reactivity, as the valence electrons are further from the nucleus and less strongly attracted.