In the Periodic Table, we call the first group Group 1, or The Alkali Metals. This Group consists of Lithium, Sodium, Potassium, Rubidium, Ceasium and Francium. However, you will only have to deal with the first three.
All Alkali Metals are reactive. They have to be stored in oils so they don't react to the oxygen in the air. Their reactivity is more aggressive as you move down the group.
- Lithium - Least Reactive