Anomalous Properties of Lithium

Introduction- Lithium

Lithium is the third element of the periodic table and belongs to the group 1 element of alkali metals. However, the element exhibits different properties than the rest of its group elements. It is a delicate silvery-white alkali metal. Under ordinary circumstances, it is the lightest metal and the lightest solid element. Because Lithium, like all alkali metals, is very reactive and flammable, it must be kept in a vacuum, inert atmosphere, or inert liquid, such as pure kerosene. It has a metallic shine when sliced, but moisture soon corrodes it to a pale silvery gray, which eventually turns to a black tarnish. It is exclusively found in (typically ionic) compounds such as pegmatite minerals and is never found naturally. The first group member frequently differs from the remaining components, and it is similar to the second element of the neighboring group on the right, which is the diagonally opposite element. The similarity between diagonal elements is called the diagonal relationship in the periodic table. As a result, Lithium closely resembles Magnesium. The unusual behaviour of Lithium that varies from the other elements of its group is known as the anomalous behaviour of Lithium. Here are the anomalous properties of Lithium:

Anomalous Properties of Lithium

Anomalous behaviour is defined as behaviour that deviates from its typical pattern. It differs from the other members of its group in several ways. Elements that possess anomalous properties have distinct characteristics and produce distinct compounds. The anomalous behaviour of Lithium is related to two factors:

• The extremely tiny size of its atoms and ions
• Its strong polarizing power (i.e., charge/ radius ratio). As a result, the covalent nature of Lithium compounds increases, which is important for being soluble in organic solvents

In addition, Lithium has a diagonal connection with Magnesium. The resemblance between Lithium and Magnesium is quite remarkable, and it originates from their comparable sizes. The following are the significant factors of resemblance:

• Lithium and Magnesium are both harder and lighter than comparable elements in their groups
• Lithium and Magnesium have a delayed reaction with water. Their oxides and hydroxides are far less soluble, and their hydroxides disintegrate when heated. By combining directly with nitrogen, both Li₃N and Mg₃N₂ create a nitride
• Li₂O and MgO do not interact with extra oxygen to form superoxide
• Lithium and magnesium carbonates quickly break down to create oxides and CO₂. Lithium and magnesium do not combine to form solid hydrogen carbonates
• LiCl and MgCl₂ are both soluble in ethanol
• LiCl and MgCl₂ are deliquescent and crystallized from an aqueous solution as hydrates LiCl₂.H₂O and MgCl₂.8H₂O, respectively

Because of the atom’s small size, Lithium has unique qualities such as strong polarising power and hydration energy. The covalent character of lithium compounds is increased as a result. Lithium’s anomalous behaviour in comparison to other alkali metals:

• Lithium is substantially more brittle. It has a greater melting point and boiling point than the other alkali metals
• Lithium is the least reactive yet the most powerful reducing agent among all alkali metals
• Unlike other alkali metals, it produces mostly monoxide, Li₂O, and nitride, Li₃N, when burned in air
• LiCl deliquesces and crystallises as LiCl hydrate LiCl.2H₂O
• Other alkali metal chlorides, on the other hand, do not produce hydrates
• Lithium hydrogen carbonate is not solid, whereas all other elements produce solid hydrogen carbonates
• Unlike other alkali metals, lithium does not create ethynide when reacting with ethyne
• When warmed, lithium nitrate produces lithium oxide, Li₂O, while most alkali metal nitrates break down to produce the equivalent nitrite

4LiNO₃ → 2Li₂O + 4NO₂ + O₂ 2NaNO₃ → 2NaNO₂ + O₂

• LiF and Li₂O are substantially less soluble in water than the comparable alkali metal compounds.

Anomalous Behaviour of Lithium

• In dry air, alkali metals fade due to oxides’ development, which then reacts with humidity to generate hydroxides. They burn intensely in oxygen and produce oxides. Lithium produces monoxide. Lithium also exhibits unusual behaviour when interacting directly with nitrogen from the air to generate the nitride, Li₃N.

4Li + O₂ → 2Li₂O (oxide)

• Lithium has the highest negative standard potential value amongst the alkali metals. Its interaction with water is much less intense than sodium, which has the lowest negative standard potential value. Lithium’s behaviour is explained by its tiny size and substantial hydration energy
• The alkali metals readily react with halogens to generate ionic halides. Lithium halides, on the other hand, are moderately covalent. It is due to lithium ion’s strong polarisation capabilities (polarisation is the distortion of the anion’s electron cloud by the cation). The Lithium-ion is relatively tiny and has a significant potential to deform the electron cloud surrounding the negative halide ion. Because anion of enormous size is easily deformed, lithium iodide is the strongest covalent halide in nature
• The alkali metals are excellent reducing agents, with Lithium being the most powerful. Lithium has the highest hydration enthalpy due to its tiny ion size, contributing to its high negative standard potential value and reducing power
• The alkali metals generate hydrides when they react with dihydrogen at 673 K and Lithium at 1073 K. Most alkali metal hydrides are ionic solids with extremely high melting points

2M + H₂ → 2M + H- 

Conclusion

An anomaly is a deviation from the usual or fundamental order of things. It differs from the other members of its group in terms of qualities. Anomalous elements have distinct characteristics and generate unique compounds. Small size, high electronegativity, and a lack of d–orbitals all contribute to the irregular behaviour of periodic table elements. Lithium is the third element in the periodic table and shows anomalous behaviour. Lithium exhibits different properties than other elements in group 1 of the periodic table. Lithium is a hard metal, while other alkali metals are soft. It has high melting and boiling points and the least reactivity amongst alkali metals. Lithium produces monoxide on reaction with oxygen, reacts with nitrogen to form nitrides, and its hydroxide and carbonate are unstable and decompose when exposed to heat.