The term “lithium” is often used broadly, leading to confusion about its chemical identity. The pure element is a soft, silvery metal, but it is rarely encountered in this form outside of laboratories. The substances commonly referred to as “lithium” are chemical compounds, many of which fit the precise definition of a salt. The difference lies between the element’s neutral atomic state and its charged ionic state.
Defining Chemical Salts
A salt is a compound formed from the reaction between an acid and a base. This neutralization results in an ionic compound composed of positively and negatively charged ions. These ions are held together by strong electrostatic forces known as ionic bonds. A salt must contain a positively charged ion (cation) and a negatively charged ion (anion), resulting in a neutral electrical charge overall.
The cation is derived from a base, while the anion originates from an acid. A familiar example is common table salt, sodium chloride (\(\text{NaCl}\)), where the sodium ion (\(\text{Na}^{+}\)) is the cation and the chloride ion (\(\text{Cl}^{-}\)) is the anion. When dissolved in water, these ionic compounds dissociate into their constituent ions, allowing the solution to conduct electricity.
The Nature of Elemental Lithium
Elemental lithium, symbolized as \(\text{Li}\), is classified as an alkali metal. It is the lightest and least dense of all solid elements, sitting at the top of Group 1 on the periodic table. As an alkali metal, it possesses a single valence electron, which it readily gives up in chemical reactions. This high reactivity means that pure lithium metal is never found naturally on Earth.
When the neutral lithium atom loses its valence electron, it forms the stable, positively charged lithium cation (\(\text{Li}^{+}\)). This ion is the fundamental building block for all lithium compounds, including its salts. The pure metal itself is not a salt because it is a single element and does not contain both a cation and an anion bonded together.
The Chemistry of Lithium Salts
When the positively charged lithium ion (\(\text{Li}^{+}\)) combines with an anion, the resulting compound fulfills the definition of a salt. The electrostatic attraction between the \(\text{Li}^{+}\) cation and the anion forms a strong ionic bond, creating a stable, neutral compound.
A widely known example is Lithium Carbonate (\(\text{Li}_2\text{CO}_3\)), where two \(\text{Li}^{+}\) cations balance the charge of the carbonate anion (\(\text{CO}_3^{2-}\)). Another common example is Lithium Chloride (\(\text{LiCl}\)), which forms when the \(\text{Li}^{+}\) cation bonds with the chloride anion (\(\text{Cl}^{-}\)). These compounds are formally salts because they are ionic structures composed of a metallic cation (\(\text{Li}^{+}\)) and an anion derived from an acid, fulfilling all structural requirements.
Common Applications of Lithium Salts
The primary uses of lithium in modern society rely heavily on the properties of its salt compounds, not the pure metal. In medicine, specific lithium salts are used to treat mood disorders, most notably bipolar disorder. The compound prescribed in this context is typically Lithium Carbonate, which is taken orally to help stabilize mood fluctuations. The therapeutic effect is attributed to the activity of the \(\text{Li}^{+}\) ion within the central nervous system.
Industrially, lithium salts are necessary for the function of modern rechargeable batteries, known as lithium-ion batteries. While the electrodes may contain lithium compounds, the electrolyte solution that conducts the charge must contain a dissolved lithium salt. Salts like lithium hexafluorophosphate (\(\text{LiPF}_6\)) or lithium chloride (\(\text{LiCl}\)) dissociate within the battery’s electrolyte to provide the mobile \(\text{Li}^{+}\) ions that shuttle back and forth between the electrodes, enabling the transfer of energy.