All six members of the alkali metals group react violently when exposed to water. When water touches alkali metals the reaction produces hydrogen gas and a strong alkaline solution, also known as a base. The further down the element lies on the periodic table, the more severe the reaction.
The six elements in the alkali metals group are, in order of appearance on the periodic table: lithium, sodium, potassium, rubidium, cesium and francium. Lithium experiences the mildest reaction with water, while francium produces the most violent explosion. Lithium floats on the surface of water, where it begins to fizz as it slowly releases hydrogen and eventually dissolves.
The next element in the group, sodium, also fizzes in water, but the reaction generates enough heat to melt the metal. The liquid sodium forms a ball that rapidly moves around the water's surface as it dissolves. This reaction also produces a small orange flame at times, as the reaction creates hydrogen gas that the heat ignites.
When potassium comes in contact with water, it experiences a more severe reaction. The metal almost instantly melts and moves around like the sodium, but this reaction usually causes the hydrogen to ignite immediately. The metal also catches fire in most cases, shooting off sparks and burning a purple color. In some cases, this reaction ends with a small explosion.
The other three members of the group all experience violent explosions to a varying degree when exposed to water.