Lithium (Li) is a soft, silvery-white alkali metal and the lightest metal on the periodic table. Its chemical behavior is dominated by its structure, possessing a single electron in its outermost shell. This configuration makes Lithium highly reactive, as it readily sheds this valence electron to achieve a stable, positive-ion state (Li+). Consequently, Lithium functions as a powerful reducing agent, aggressively seeking out other elements to form chemical bonds.
Lithium’s Dramatic Reaction with Water and Air
Lithium reacts energetically with moisture and gases present in the surrounding environment. When exposed to water, a vigorous reaction occurs, producing Lithium Hydroxide (LiOH) and releasing highly flammable hydrogen gas (H2). This reaction is exothermic, generating heat, and the hydrogen gas released can spontaneously ignite. The reaction is forceful, and the metal will float on the water’s surface due to its extremely low density.
Exposing Lithium to air quickly results in the metal tarnishing from a shiny silver to a dull, dark gray or black. This happens because it rapidly reacts with both oxygen and nitrogen components in the air. The primary reaction with oxygen forms Lithium Oxide (Li2O), which contributes to the dark surface coating.
A unique reaction among the alkali metals is Lithium’s ability to react with atmospheric nitrogen (N2) at room temperature. This forms the stable compound Lithium Nitride (Li3N), a dark-colored solid that also contributes to the tarnish. This ability is a consequence of Lithium’s small size, which allows the resulting Li+ ion to stabilize the Lithium Nitride crystal structure through strong lattice energy.
Forming Compounds with Halogens and Other Elements
Lithium exhibits a strong chemical affinity for non-metallic elements, especially the Halogens. It reacts vigorously with all members of the halogen group, including fluorine, chlorine, bromine, and iodine, to produce Lithium Halides (salts like LiCl or LiBr). These reactions are highly exothermic, releasing a significant amount of energy. The resulting compounds are white, crystalline ionic solids, driven by the electrostatic attraction between the Li+ ion and the negative halide ion.
Lithium also reacts with other non-metals like sulfur and phosphorus, generally requiring higher temperatures to initiate the reaction. For instance, a reaction with sulfur yields Lithium Sulfide (Li2S), a compound that shares the ionic characteristics of the halides.
Lithium metal reacts readily with acids, similar to its reaction with water, but with far greater intensity. When reacting with acids, Lithium displaces the hydrogen, creating a Lithium salt and releasing hydrogen gas. For example, reacting with hydrochloric acid (HCl) produces Lithium Chloride (LiCl) and hydrogen gas (H2). The presence of water in most acid solutions means this reaction is exceptionally energetic.
The Practical Necessity of Safe Lithium Storage
The extreme reactivity of Lithium dictates strict handling and storage protocols in all laboratory and industrial settings. Because it reacts immediately with both moisture and oxygen, Lithium metal cannot be stored in the open air. Its low density means it floats on kerosene and mineral oil, which are the standard storage liquids for other alkali metals.
To prevent unwanted reactions, Lithium metal is typically stored submerged in hydrocarbons that exclude both water and oxygen, such as mineral oil, paraffin wax, or specialized petroleum ether. This protective environment prevents the metal from reacting to form Lithium Oxide or Lithium Nitride. In specialized applications, Lithium may be stored under an inert gas like Argon or Helium inside a glove box. Nitrogen is avoided in these inert atmospheres because Lithium is one of the few metals that reacts with it at ambient conditions.