The most reactive metals are found in Group 1 of the periodic table, specifically known as the alkali metals. This group includes lithium, sodium, potassium, rubidium, cesium, and francium. These metals are characterized by having a single electron in their outermost shell, which they readily lose to form positive ions.
Their high reactivity is most noticeable when they come into contact with water or air. For instance, sodium reacts vigorously with water, producing sodium hydroxide and hydrogen gas. As you move down the group from lithium to francium, the reactivity increases. This trend is due to the increasing atomic size, which causes the outer electron to be farther from the nucleus and less tightly held, making it easier to lose.
On the other hand, the most reactive non-metals can be found in Group 17, known as the halogens. The combined understanding of these groups helps illustrate the periodic trends in reactivity among metals and non-metals.