The gas released when Group 1 elements (alkali metals) react with water is hydrogen gas (H₂). When these metals—such as lithium, sodium, potassium, rubidium, and cesium—come into contact with water, they react vigorously to produce an aqueous metal hydroxide and hydrogen gas. The general reaction is:
2X(s)+2H2O(l)→2XOH(aq)+H2(g)2X(s)+2H_2O(l)\rightarrow 2XOH(aq)+H_2(g)2X(s)+2H2O(l)→2XOH(aq)+H2(g)
where XXX represents the Group 1 metal. The hydrogen gas is released as bubbles, and this reaction is often exothermic, sometimes producing enough heat to ignite the hydrogen gas, causing a flame or even an explosion depending on the metal involved. The metal hydroxides formed make the water alkaline due to the hydroxide ions. This behavior intensifies down the group from lithium to cesium, with reactivity and the vigor of hydrogen gas release increasing accordingly.
