Uncoated lithium metal reacts with water to form a colorless lithium hydroxide solution and hydrogen gas. The resulting solution is basic because of the resulting hydroxide ions. The reaction is both spontaneous and exothermic, but the amount of heat produced is lower than other metals in group 1A.
The reaction of lithium with water to produce a metal hydroxide and hydrogen is called hydrolysis. All elements of group 1A undergo hydrolysis when placed in water because of their high electropositivity. The electrons of the outer shells of this group are weakly attracted to the nucleus, being shielded from nuclear charge by the inner shells of electrons. These outer electrons are readily ejected from the atom in chemical reactions, producing a positive ion having the same electronic configuration as the nearest noble gas.
When exposed to water, surface atoms of lithium shed their outer electrons. Water molecules near the lithium surface dissociate into H– and –OH groups. The negatively charged –OH groups bond ionically with positively charged lithium ions, producing lithium hydroxide, which is water soluble and dissociates back into its ionic form immediately upon formation. Meanwhile, each two positive H– groups acquire two electrons and bond together covalently to form molecular hydrogen. When enough hydrogen gas molecules come together, they form a bubble that evolves from the solution.