Anomalous Properties of Lithium

 

Table of Content

Introduction about Lithium Nature of Lithium Uses of Lithium Difference between lithium and other alkali metals

 

Introduction about Lithium

Group 1 elements of the periodic table are known as Alkali Metals. Lithium is the first element of the group 1. The small size of lithium allows it to behave differently from other alkali elements (Anomalous behavior).
 

Nature of Lithium

Lithium is highly electropositive in nature which allows it to form covalent bonds. The polarization behavior of lithium ion is comparable to that of magnesium ion. Thus, lithium shows a diagonal relationship with magnesium. There are various reasons for diagonal relationship of lithium with magnesium. These reasons are as follows:

• As one moves from top to bottom in a group, electropositive nature increases. But from left to right in a period, electropositive nature decreases. Due to this, similar properties are observed between diagonal elements.

• From top to bottom in a group, size increases; due to this polarizing power decreases but moving left to right in period polarizing power increases, thus diagonal elements show similar properties.

• Lithium is a strong element similar to magnesium.

• Lithium and magnesium ion show comparable boiling and melting points.

• Due to small size, the lithium atom has high ionization energy. It reacts with water, liquid bromine and forms a highly stable hydride unlike other alkali metals. Magnesium exhibits all these properties.

Fig. 1. Reasons for Diagonal Relationship

• Lithium and magnesium both forms monoxides.

2Mg + O₂→ 2MgO

• Lithium and magnesium both reacts with nitrogen to form lithium nitride and magnesium nitride.

(s) + N₂(g) → 2Li₃N(s)

• Lithium and magnesium both reacts slowly with water and form oxides and hydroxides which decompose on heating.

Mg(s) + 2H₂O(g) → Mg(OH)₂(aq) + H₂(g)

• Oxides of both lithium and magnesium do not form superoxides.

• The carbonates of lithium and magnesium decompose on heating to form the oxides and carbon-dioxide.

2 Mg(s) + CO₂  2 MgO(s) + C(s)

• Lithium chloride (LiCl) and magnesium chloride (MgCl₂) both are soluble in ethanol.

• Both LiCl and MgCl₂ are deliquescent and form hydrates LiCl·2H₂O and MgCl₂·8H₂O.

• Both magnesium and lithium are less stable towards heat.
   

Uses of Lithium

 

Fig. 2. Uses of Lithium

Difference between Lithium and Other Alkali Metals

• Lithium is harder than other alkali metals.

• Melting and boiling point is higher than other alkali metals.

• Lithium is least reactive out of all alkali metals.

• It is a strong reducing agent compared to other alkali metal.

It is the only alkali metal that form the monoxide, Li₂O.

4Li_(s) + O₂(g) → 2Li₂O_(s)

• Unlike other alkali metals, it forms Li₃N.

6 Li + N₂→ 2 Li₃N

• It does not form solid hydrogen carbonates compared to other alkali metals.

• Lithium does not react with ethyne to form ethynide. But all other alkali metals form ethynide.

• Lithium nitrate on heating form lithium monoxide as compared to other alkali metals which forms nitrites on decomposition.

4 LiNO₃→ 2 Li₂O + 4NO₂ + O₂

• Lithium reacts slowly with bromine as compared to other alkali metals.

• Lithium when heated in NH₃ forms amide, Li₂ NH while other alkali metals form amides, MNH_2. M can be other alkali metals. 

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