The group 1 of the periodic table contain six elements namely Lithium(Li), Sodium(Na),Potassium(K),Rubidium(Rb),Cesium(Cs) and Francium(Fr). These metals are called alkali metals because they form alkalies( i.e. strong bases capable of neutralizing acids) when they react with water.
These metals are soluble in water and form metallic hydroxides and evolve hydrogen gas. These hydroxide are called alkalies. Therefore the elements of group IA are called alkali metals.