In the periodic table, Group 1 elements, which include lithium, sodium, potassium, rubidium, francium, and cesium, are alkali metals. Group 2 elements, which include beryllium, magnesium, calcium, strontium, and barium, are the alkaline earth metals. Lithium is the first element of Group 1, and Beryllium is the first element of Group 2 in the periodic table. Have you ever wondered what are the anomalous properties of lithium and beryllium, and why do they behave so differently?
Well, the reason for the anomalous behaviour of lithium and beryllium is their small size. Here you will see what the properties of lithium and beryllium are and how they behave differently from other group elements.
The size of the atoms generally increases in a group while moving from top to bottom. Due to this reason, the polarizing power of the atoms decreases. Hence, lithium is the element that has a small size and high polarizing power. Additionally, lithium is tremendously electropositive in nature due to which it can form covalent bonds. To sum up, the anomalous behaviour of lithium as compared to other alkali metals is due to the following reasons:
High polarizing power
Covalent nature of lithium compounds
Nature: Lithium is much harder compared to other alkali metals.
Melting and Boiling Point: The melting and boiling point of lithium is higher as compared to other group elements.
Reactivity: Out of all the alkali metals, lithium is the least reactive metal.
Oxidation: Lithium is a strong reducing agent and hence a weak oxidizing agent in comparison to other alkali metals.
Solubility: The lithium compounds are moderately soluble in water in comparison to other alkali metals, which are extremely soluble in water.
Chemical Reactions: Lithium is the only alkali metal, which can form its monoxide. However, it is not capable of forming solid hydrogen carbonates. All the alkali metals can form ethynide except lithium, which does not react with ethyne. Moreover, it shows a slow reaction with bromine as compared to other group elements.
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Lithium has the smallest size in the alkali metal series. Along with it, lithium has a high polarization power. These properties of the lithium are similar to magnesium, which is diagonally placed in the next series. Both elements show following same properties:
The lithium and magnesium ions have comparable melting and boiling points.
They both form monoxides:
2Mg + O2 → 2MgO
They form nitrides by reacting with nitrogen:
Li(s) + N2(g) → 2Li3N(s)
They both form hydroxides and oxides by slowly reacting with water:
Mg(s) + 2H2O(g) → Mg(OH)2(aq) + H2(g)
Both LiCl and MgCl2 are soluble in ethanol.
The major reasons for the anomalous properties of beryllium are as follow:
Small atomic and ionic size
High ionization energy
Absence of d-orbital
Hence, there is an anomalous behaviour of beryllium that can be observed.
Nature: Beryllium is quite much harder as compared to other group members.
Melting and Boiling Point: As compared to other alkali metals, Beryllium has higher melting and boiling points.
Reaction: All the members of group 2 react with water to form oxides or hydroxides except Beryllium. It does not react with water even at extraordinary temperatures.
Compound Formation: The group 2 members form ionic compounds as compared to Beryllium, which forms covalent compounds. Due to the covalent character, beryllium salts are certainly hydrolyzed (the bond breaks down when it reacts with water).
Beryllium Carbides: Generally, the carbides of Beryllium are covalent in nature instead of other member carbides, which are ionic. Additionally, Beryllium Carbide can react with water to produce methane gas. However, carbide of other alkaline metals produces acetylene gas.
Coordination Number: Beryllium exhibits coordination number of 4, whereas other alkaline earth metals can exhibit a coordination number of 6. It is because the valence shell of Beryllium has only 4 orbitals, namely; 1 s and p. That is why; it cannot show the coordination number of more than 4. However, other group elements can make use of d-orbitals and hence can exhibit a coordination number of 6.
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The oxides of both Beryllium and Aluminium are amphoteric in nature; that is, they show both acidic and basic nature. Both elements have the same polarizing power as well as electronegativity. Additionally, they both show reducing character due to which they exhibit the following properties similar:
Both AlCl₃ and BeCl₂ act as Lewis acids and have chlorine-bridged structures in the vapor phase.
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Due to the formation of protective film on the surface, both Be and Al are resistant to exploit of acids.
Both Beryllium and Aluminium dissolve in the strong alkalies and form soluble complexes.
Both the metals can form complexes due to similar polarizing power.
Hence, the anomalous properties of lithium and beryllium are due to their small size.
1. What Physical Properties are Common in Lithium and Beryllium?
Though Lithium and Beryllium belong to two different groups in the periodic table, both have some similarities in them. These are partially soluble in the water and exhibit large atomic radii. Both of them have small size and thus they have better ionizing energy and also they both form a stable hydride than any other alkali metal. Both of these metals show anomalous behaviour due to their high electronegativity and high polarizing power.
2. Can Lithium React with Oxygen?
If brought in contact with air and fire, lithium reacts and burns with red-tinged flame. Lithium forms lithium oxide when burnt in the presence of oxygen. Also, when brought in contact with the nitrogen, lithium forms Lithium Nitride. However, the burning flame is very intense in the case of lithium burns with oxygen. The reaction of burning in oxygen is as follows:
4Li + O2 → 2Li2O
The reaction of Lithium with nitrogen is as follows:
6Li + N2 → 2Li3N
Also, only Lithium exhibits the property of forming Nitrides in its group of the periodic table.