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Beryllium

  • Atomic Number: 4
  • Atomic Weight: 9

  • Electronic Configuration: 1s2 2s2

  • Valency : 2

Physical Properties of Beryllium

Property 

Value 

Density 

1.85 g/cm3

Melting point

1560 K (1287°C, 4476°F)

Boiling point

2742 K (2469°C, 4476°F)

Heat of fusion

7.895 kJ/mol

Heat of vaporization

297 kJ/mol

Heat capacity

(25°C) 16.443 J/(mol/K)

Refer to the follwoing video for the structure of beryllium atom

Anomalous Behaviour of Beryllium    

Some important points of difference between beryllium and other members (especially magnesium) are given below:                

  • Be is harder than other members of its group.

  • Be is lighter than Mg.

  • Be does not react with water while Mg reacts with boiling water.

  • BeO is amphoteric while MgO is weakly basic.

  • Its melting and boiling points are higher than those of Mg & other members.

  • Be forms covalent compounds whereas other members form ionic compounds.

  • Beryllium carbide reacts with water to give methane whereas carbides of other alkaline earth metals gives acetylene gas.
    Be2C + 4H2O → 2Be (OH)2 + CH4
    Mg2C2 + 2H2O → Mg (OH)2 + C2H2        
    CaC2 + 2H2O → Ca (OH)2 + C2H2       

  • Beryllium does not exhibit coordination number more than four as it has four orbitals in the valence shell. The other members of this group has coordination number 6. 

Reason for the anamolus behaviour of beryllium

The properties of berrylium the first member of the alkaline earth metal, differ from the rest of the member. Its is mainly because of

  • Its small size and high polarizing power.

  • Relatively high electro negativity and ionization energy as compared to other members.

  • Absence of vacant d – orbitals in its valence shell. 

Resemblance of Beryllium with Aluminium (Diagonal Relationship)

The following points illustrate the anomalous behaviour of Be and its resemblance with Al.

  • Unlike groups – 2 elements but like aluminium, beryllium forms covalent compounds.

  • The hydroxides of Be, [Be(OH)2] and aluminium [Al(OH)3] are amphoteric in nature, whereas those of other elements of group – 2 are basic in nature.

  • The oxides of both Be and Al i.e. BeO and Al2O3 are high melting insoluble solids.

  • BeCl2 and AlCl3 have bridged chloride polymeric structure.
    538_Anamolous Behaviour of Beryllium.JPG

  • The salts of beryllium as well as aluminium are extensively hydrolysed.

  • Carbides of both the metal reacts with water liberating methane gas.
    Be2C + 4H2O → 2Be (OH)2 + CH4       
    AI4C3 + 12H2O → 4Al (OH)3 + 3CH4      

  • The oxides and hydroxides of both Be and Al are amphoteric and dissolve in sodium hydroxide as well as in hydrochloric acid.
    BeO + 2HCl → BeCl2 + H2O       
    BeO + 2NaOH → Na2BeO+ H2O       
    Al2O+ 6HCl → 2AlCl3 + H2O      

  • Like Al, Be is not readily attacked by acids because of the presence of an oxide film.

Illustration:

Question: Give the structure of BeCl2 in the

  • Vapour state

  • Solid state

Solution:

  • Linear molecule

  • Polymeric structure with bridged chlorine atom

303_Solution.JPG

Uses of Beryllium

  • Alloys of beryllium with copper or nickel are used for making gyroscopes, springs, electrical contacts, spot-welding electrodes and non-sparking tools.

  • Mixing beryllium with any metal to form alloy increases their electrical and thermal conductivity.  

  • Some alloys of beryllium are used as structural materials for high-speed aircraft, missiles, and spacecraft and communication satellites also. 

  • Beryllium is used in X –ray lithography also as it  is transparent to X-rays

Question 1: Which of the following is not the correct reason for anomalous property of Be?

a. Its small size and high polarizing power.

b. Relatively high electro negativity and ionization energy as compared to other members.

c. Absence of vacant d – orbitals in its valence shell. 

d. Presence of fully filled 2s orbital

Question 2: Which of the following statements is incorrect?

a. Be is harder than other members of its group.

b. Be is lighter than Mg.

c. Be does not react with water while Mg reacts with boiling water.

d. BeO is acidic while MgO is amphoteric.

Question 3: BeO + 2HCl →

a.  BeCl2 + H2

b.  BeCl + H2O +Cl2

c.  BeCl2 + Cl2

d. BeCl2 + H2

Question 4: Be is not readily attacked by acids because of the presence of 

a. an oxide film

b. empty d orbitals

c. fully filled 2s orbital

d. lone pair of electrons

Q.1

Q.2

Q.3

Q.4

d

d

a

a

Related Resources

To read more, Buy study materials of S- Block elements comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.

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