Notes on Anomalous Behaviour of Beryllium | Class 12

Beryllium is the first alkaline earth metal having an atomic number of 5. Its atomic size is very small about 153 pm. In this article learn anomalous behavior of beryllium.

Why beryllium shows strange behavior

1. Small atomic size
2. High electronegativity value so that beryllium behaves differently than other alkaline earth elements.

Anomalous Behaviour of Beryllium

1. Beryllium has a high charge density due to its small atomic size. It shows a strong tendency to form covalent compounds. Hence the salts of beryllium are soluble in organic solvents and have a low melting point. 

If you consider the other alkaline earth elements then they do not form covalent compounds.

Beryllium chloride - a covalent compound

2. When alkaline earth elements added to water decompose the water. But beryllium does not decompose water due to a weak electronegative character.

3. Beryllium reacts very slowly with dilute mineral acids and liberates hydrogen. But if we consider other alkaline earth elements, they react vigorously with dilute acids.

4. Only beryllium reacts with concentrated HNO3 becomes passive i.e resistant to the attack of the con. HNO3. This happens because the inert oxide film is formed on the surface of beryllium. 

2HNO3 + H2O → 2NO2 O
Be + O → BeO

5. When alkaline earth metals react with oxygen to form oxides. Beryllium oxide is extremely hard, non-volatile, and has a very high melting point of about 2780 K (2507 ℃). 

6. Beryllium oxide or hydroxide is amphoteric in nature. But oxides or hydroxides of other alkaline earth metals are basic in nature.

Beo + 2HCl → BeCl2 + H2O
BrO + 2NaOH + Na2BeO2 + H2O

7. Only beryllium carbide gives methane on hydrolysis and not the carbides of other alkaline earth elements.

Be2C + 4H2O → 2Be(OH)2

But on similar treatment other alkaline earth elements give acetylene

8. Beryllium forms polymeric covalent hydrides in the vapor phase. But the hydrides of other alkaline earth elements are electrovalent.

9. When oxides beryllium with other metal oxides form transparent beads which look like a precious stone like beryl and sapphire. But other alkaline earth elements do not form such stones.

10. Only beryllium forms many chelate type complexes, especially with oxygen donors. But other alkaline earth elements do not.

11. Beryllium salts are extensively hydrolyzed. because its salts have never more than four molecules of water of crystallization. 

It is because of the availability of only four orbitals in the second shell.

These properties show the anomalous behavior of beryllium.