Here's why:
* Low Ionization Energies: These metals readily lose their outermost electron(s) to form positive ions. This ease of losing electrons is what defines their reactivity.
* Strong Reducing Agents: They are strong reducing agents, meaning they readily donate electrons to other substances.
* Reactivity Increases Down the Group: As you move down the group, the outermost electrons are further from the nucleus and easier to remove, leading to increasing reactivity.
Examples:
* Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) (Group 1)
* Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) (Group 2)
Note: These metals are highly reactive and must be handled with care. They react violently with water and air, and are often stored in oil or inert atmospheres.
