Beryllium is the first alkaline earth metal having an atomic number 5. Its atomic size is very small about 153 pm. On the other hand, electronegativity value is very high about 1.57 which is greater than lithium but less than boron.
The properties of beryllium are determined by these factors
Physical properties of beryllium
|Melting point||1560 K|
|Boiling point||2742 K|
|Heat of vapourization||12.2 KJ/mole|
|Heat of fusion||292 KJ/mole|
If you compare beryllium with other family elements, then the electronegativity value is higher.
These are two reasons small atomic size and high electronegativity value so that beryllium behaves differently than other alkaline earth elements.
Now let’s get into the points which make beryllium different than other alkaline earth group elements.
#1 Beryllium has a high charge density due to 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.
#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 rigorously 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 → 2NO2O
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 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.
#7 Only beryllium carbide gives methane on hydrolysis and not the carbides of other alkaline earth elements.
Be2C + 4H2O → 2Be(OH)2
#8 Beryllium forms polymeric covalent hydrides in the vapor phase. But the hydrides of other alkaline earth elements are electrovalent.
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.