Alkali metal is a term that refers to six elements: lithium, sodium, potassium, rubidium, cesium, and francium.
These elements make up group I of the periodic table of elements.
They all form singly-charged positive ions, and are extremely reactive.
They react violently with water, forming hydroxides and releasing hydrogen gas and heat.
Cesium and francium are the most reactive and lithium is the least.