Chapter : The-p-block-element - Class 12 PDF Download

 Page 1


133 
 
CHAPTER 11 
The p-block elements 
Elements in which the last electron enters in the any one of the three p- orbital of 
their outermost shells – p-block elements 
•
 Gen. electronic configuration of outer shell is  ns
2
np
1-6 
The inner core of e-config.may differ which greatly influences their physical & to 
some extent chemical properties. 
• The block of elements in the periodic table consisting of the main groups : 
• Group 13         (B to Tl) 
• Group14        (C to Pb) 
•  Group15         (N to Bi)  
• Group 16         (O to Po) 
• Group17        (F to At) 
• Group18   (He to Rn) 
(1)   Members at the top and on the right of the p-block are nonmetals (C, N,   P, O, 
F, S, Cl, Br, I, At).  
(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).  
(3)    Between the two, from the top left to bottom right, lie an ill-defined group of 
metalloid elements (B, Si, Ge, As, Te) 
GROUP 13  :  The boron group 
 Outer Electronic Configuration:-ns
2
np
1
 
• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& 
thallium (Tl) .             All, except boron, are metals. 
• Boron show diagonal relationship with Silicon;  both are semiconductors 
metalloids & forms covalent compounds. 
•  Boron compounds are electron deficient, they are lack of an octet of electrons 
about the B atom . 
• diborane  B
2
H
6
, is  simplest boron hydride 
Page 2


133 
 
CHAPTER 11 
The p-block elements 
Elements in which the last electron enters in the any one of the three p- orbital of 
their outermost shells – p-block elements 
•
 Gen. electronic configuration of outer shell is  ns
2
np
1-6 
The inner core of e-config.may differ which greatly influences their physical & to 
some extent chemical properties. 
• The block of elements in the periodic table consisting of the main groups : 
• Group 13         (B to Tl) 
• Group14        (C to Pb) 
•  Group15         (N to Bi)  
• Group 16         (O to Po) 
• Group17        (F to At) 
• Group18   (He to Rn) 
(1)   Members at the top and on the right of the p-block are nonmetals (C, N,   P, O, 
F, S, Cl, Br, I, At).  
(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).  
(3)    Between the two, from the top left to bottom right, lie an ill-defined group of 
metalloid elements (B, Si, Ge, As, Te) 
GROUP 13  :  The boron group 
 Outer Electronic Configuration:-ns
2
np
1
 
• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& 
thallium (Tl) .             All, except boron, are metals. 
• Boron show diagonal relationship with Silicon;  both are semiconductors 
metalloids & forms covalent compounds. 
•  Boron compounds are electron deficient, they are lack of an octet of electrons 
about the B atom . 
• diborane  B
2
H
6
, is  simplest boron hydride 
134 
 
• Structure: three-center two-electron: the H atoms are simultaneously bonded to 
two B atoms the B-H bridging bond lengths are greater than B-H terminal. 
• - Boron oxide is acidic (it reacts readily with water to form boric acid) 
• aluminium compounds:aluminium oxide is amphoteric  
• aluminum halides, e.g., AlCl
3
 is dimer, an important catalyst in organic 
chemistry have anincomplete octet, acts as Lewic acid by accepting lone pairs 
from Lewic bases, forming adduct 
• aluminum hydride, e.g., LiAlH
4
, a reducing agent 
• Atomic Properties - Electronic Configurations 
Element Symbol Atomic 
No. 
Electronic 
Configuration 
Abundance in Earth’s 
Crest (in ppm) 
Boron B 5 [He]2s
2
 2p
1
 8 
Aluminium Al 13 [Ne]3s
2
 3p
1
 81,300 
Galium Ga 31 [Ar]3d
10
4s
2
 4p
1
 15 
Indium In 49 [Kr] 4d
10
5s
2
 5p
1
 1 
Thallium Tl 81 [Xe] 5d
10
6s
2
 6p
1
 0.3 
 
. Atomic and ionic radii 
• The atomic and ionic radii of group 13 elements are compared to 
corresponding elements of group 2.   From left to right in the period, the 
magnitude of nuclear charge increases but the electrons are added to, the same 
shell.  These electrons do not screen each other, therefore, the electrons 
experience greater nuclear charge. 
•  In other words, effective nuclear charge increases and thus, size decreases. 
Therefore, the elements of this group have smaller size than the corresponding 
elements of second group. 
• On moving down the group both atomic and ionic radii are expected to 
increase due to the addition of new shells. However, the observed atomic 
radius of Al (143 pm) is slightly more than that of Ga (l35 pm). 
Ionization energies 
The first ionization energies of group 13 elements are less than the corresponding 
members of the alkaline earths.  
Page 3


133 
 
CHAPTER 11 
The p-block elements 
Elements in which the last electron enters in the any one of the three p- orbital of 
their outermost shells – p-block elements 
•
 Gen. electronic configuration of outer shell is  ns
2
np
1-6 
The inner core of e-config.may differ which greatly influences their physical & to 
some extent chemical properties. 
• The block of elements in the periodic table consisting of the main groups : 
• Group 13         (B to Tl) 
• Group14        (C to Pb) 
•  Group15         (N to Bi)  
• Group 16         (O to Po) 
• Group17        (F to At) 
• Group18   (He to Rn) 
(1)   Members at the top and on the right of the p-block are nonmetals (C, N,   P, O, 
F, S, Cl, Br, I, At).  
(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).  
(3)    Between the two, from the top left to bottom right, lie an ill-defined group of 
metalloid elements (B, Si, Ge, As, Te) 
GROUP 13  :  The boron group 
 Outer Electronic Configuration:-ns
2
np
1
 
• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& 
thallium (Tl) .             All, except boron, are metals. 
• Boron show diagonal relationship with Silicon;  both are semiconductors 
metalloids & forms covalent compounds. 
•  Boron compounds are electron deficient, they are lack of an octet of electrons 
about the B atom . 
• diborane  B
2
H
6
, is  simplest boron hydride 
134 
 
• Structure: three-center two-electron: the H atoms are simultaneously bonded to 
two B atoms the B-H bridging bond lengths are greater than B-H terminal. 
• - Boron oxide is acidic (it reacts readily with water to form boric acid) 
• aluminium compounds:aluminium oxide is amphoteric  
• aluminum halides, e.g., AlCl
3
 is dimer, an important catalyst in organic 
chemistry have anincomplete octet, acts as Lewic acid by accepting lone pairs 
from Lewic bases, forming adduct 
• aluminum hydride, e.g., LiAlH
4
, a reducing agent 
• Atomic Properties - Electronic Configurations 
Element Symbol Atomic 
No. 
Electronic 
Configuration 
Abundance in Earth’s 
Crest (in ppm) 
Boron B 5 [He]2s
2
 2p
1
 8 
Aluminium Al 13 [Ne]3s
2
 3p
1
 81,300 
Galium Ga 31 [Ar]3d
10
4s
2
 4p
1
 15 
Indium In 49 [Kr] 4d
10
5s
2
 5p
1
 1 
Thallium Tl 81 [Xe] 5d
10
6s
2
 6p
1
 0.3 
 
. Atomic and ionic radii 
• The atomic and ionic radii of group 13 elements are compared to 
corresponding elements of group 2.   From left to right in the period, the 
magnitude of nuclear charge increases but the electrons are added to, the same 
shell.  These electrons do not screen each other, therefore, the electrons 
experience greater nuclear charge. 
•  In other words, effective nuclear charge increases and thus, size decreases. 
Therefore, the elements of this group have smaller size than the corresponding 
elements of second group. 
• On moving down the group both atomic and ionic radii are expected to 
increase due to the addition of new shells. However, the observed atomic 
radius of Al (143 pm) is slightly more than that of Ga (l35 pm). 
Ionization energies 
The first ionization energies of group 13 elements are less than the corresponding 
members of the alkaline earths.  
135 
 
The sharp decrease in I.E. from B to Al is due to increase in size. In case of Ga, there 
are ten d-electrons in its inner electronic configuration.  
The very high value of 3
rd
 I. E. of thallium indicates that +3 O.N. state is not stable, 
rather +1 is more stable for thallium . 
Electropositive (or metallic) character 
the elements of group 13 are less electropositive as compared to elements of group 2. 
On moving down the group the electropositive (metallic) character increases because 
ionization energy decreases. For e.g., Boron is a non-metal white the other elements 
are typical metals.  
Oxidation states 
The common oxidation states of group 13 elements are +3 and + l .The stability of 
the + 1 oxidation state increases in the sequence Al <Ga< In <Tl, Due to Inert pair 
effect. 
        
 
 
Chemical reactivity of Gr.13 Elements 
All elements in their compounds exhibit the oxidation state of + 3 and +1. 
Hydrides 
• None of the group 13 elements reacts directly with hydrogen. However, a no. 
of hydrides of these elements have been prepared by indirect methods. The 
boron hydrides are called boranes& classified in two series:   (a)         B
n
H
n+4
 
called nidoboranes             (b)       B
n
H
n+6
 called arachnoboranes 
• INUDUSTRIAL PREPERATION :- 
2BF
3
(g) + 6LiH(s) ? B
2
H
6
(g)  + 6LiF(s) 
• Laboratory method: 
(i) By the reaction of iodine with sodium borohydride in a high boiling 
solvent.    
2NaBH
4  
+ I
2
  ? B
2
H
6
  + 2NaI    + H
2
   
(ii) By reduction of BCl
3
 with LiAlH
4  
        
4BCl
3
  +  3LiAlH
4  
? 2 B
2
H
6 
 + 3AlCl
3
  + 3 LiCl 
Element B Al Ga In Tl 
Oxidation state +3 +3 +3, +1 +3, +1 +3, +1 
 
Page 4


133 
 
CHAPTER 11 
The p-block elements 
Elements in which the last electron enters in the any one of the three p- orbital of 
their outermost shells – p-block elements 
•
 Gen. electronic configuration of outer shell is  ns
2
np
1-6 
The inner core of e-config.may differ which greatly influences their physical & to 
some extent chemical properties. 
• The block of elements in the periodic table consisting of the main groups : 
• Group 13         (B to Tl) 
• Group14        (C to Pb) 
•  Group15         (N to Bi)  
• Group 16         (O to Po) 
• Group17        (F to At) 
• Group18   (He to Rn) 
(1)   Members at the top and on the right of the p-block are nonmetals (C, N,   P, O, 
F, S, Cl, Br, I, At).  
(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).  
(3)    Between the two, from the top left to bottom right, lie an ill-defined group of 
metalloid elements (B, Si, Ge, As, Te) 
GROUP 13  :  The boron group 
 Outer Electronic Configuration:-ns
2
np
1
 
• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& 
thallium (Tl) .             All, except boron, are metals. 
• Boron show diagonal relationship with Silicon;  both are semiconductors 
metalloids & forms covalent compounds. 
•  Boron compounds are electron deficient, they are lack of an octet of electrons 
about the B atom . 
• diborane  B
2
H
6
, is  simplest boron hydride 
134 
 
• Structure: three-center two-electron: the H atoms are simultaneously bonded to 
two B atoms the B-H bridging bond lengths are greater than B-H terminal. 
• - Boron oxide is acidic (it reacts readily with water to form boric acid) 
• aluminium compounds:aluminium oxide is amphoteric  
• aluminum halides, e.g., AlCl
3
 is dimer, an important catalyst in organic 
chemistry have anincomplete octet, acts as Lewic acid by accepting lone pairs 
from Lewic bases, forming adduct 
• aluminum hydride, e.g., LiAlH
4
, a reducing agent 
• Atomic Properties - Electronic Configurations 
Element Symbol Atomic 
No. 
Electronic 
Configuration 
Abundance in Earth’s 
Crest (in ppm) 
Boron B 5 [He]2s
2
 2p
1
 8 
Aluminium Al 13 [Ne]3s
2
 3p
1
 81,300 
Galium Ga 31 [Ar]3d
10
4s
2
 4p
1
 15 
Indium In 49 [Kr] 4d
10
5s
2
 5p
1
 1 
Thallium Tl 81 [Xe] 5d
10
6s
2
 6p
1
 0.3 
 
. Atomic and ionic radii 
• The atomic and ionic radii of group 13 elements are compared to 
corresponding elements of group 2.   From left to right in the period, the 
magnitude of nuclear charge increases but the electrons are added to, the same 
shell.  These electrons do not screen each other, therefore, the electrons 
experience greater nuclear charge. 
•  In other words, effective nuclear charge increases and thus, size decreases. 
Therefore, the elements of this group have smaller size than the corresponding 
elements of second group. 
• On moving down the group both atomic and ionic radii are expected to 
increase due to the addition of new shells. However, the observed atomic 
radius of Al (143 pm) is slightly more than that of Ga (l35 pm). 
Ionization energies 
The first ionization energies of group 13 elements are less than the corresponding 
members of the alkaline earths.  
135 
 
The sharp decrease in I.E. from B to Al is due to increase in size. In case of Ga, there 
are ten d-electrons in its inner electronic configuration.  
The very high value of 3
rd
 I. E. of thallium indicates that +3 O.N. state is not stable, 
rather +1 is more stable for thallium . 
Electropositive (or metallic) character 
the elements of group 13 are less electropositive as compared to elements of group 2. 
On moving down the group the electropositive (metallic) character increases because 
ionization energy decreases. For e.g., Boron is a non-metal white the other elements 
are typical metals.  
Oxidation states 
The common oxidation states of group 13 elements are +3 and + l .The stability of 
the + 1 oxidation state increases in the sequence Al <Ga< In <Tl, Due to Inert pair 
effect. 
        
 
 
Chemical reactivity of Gr.13 Elements 
All elements in their compounds exhibit the oxidation state of + 3 and +1. 
Hydrides 
• None of the group 13 elements reacts directly with hydrogen. However, a no. 
of hydrides of these elements have been prepared by indirect methods. The 
boron hydrides are called boranes& classified in two series:   (a)         B
n
H
n+4
 
called nidoboranes             (b)       B
n
H
n+6
 called arachnoboranes 
• INUDUSTRIAL PREPERATION :- 
2BF
3
(g) + 6LiH(s) ? B
2
H
6
(g)  + 6LiF(s) 
• Laboratory method: 
(i) By the reaction of iodine with sodium borohydride in a high boiling 
solvent.    
2NaBH
4  
+ I
2
  ? B
2
H
6
  + 2NaI    + H
2
   
(ii) By reduction of BCl
3
 with LiAlH
4  
        
4BCl
3
  +  3LiAlH
4  
? 2 B
2
H
6 
 + 3AlCl
3
  + 3 LiCl 
Element B Al Ga In Tl 
Oxidation state +3 +3 +3, +1 +3, +1 +3, +1 
 
136 
 
                                                       
Structure of Diborane, B
2
H
6 
 
 
Some important characteristics of boranes: 
 i) Lower boranes are colourless gases while higher boranes are volatile liquids 
or solids. 
           ii) They undergo spontaneous combustion in air due to strong affinity of boron      
                for oxygen. 
           B
2
H
6
  + 3O
2
  ? B
2
O
3
  + 3H
2
O + Heat 
    iii) Boranes react with alkali metal hydrides in diethyl ether to form    
borohydride complexes.  
      B
2
H
6
  + 2MH ?2M
+
[BH
4
]
-
  (M= Li or Na) 
                              Metal borohydride 
• (iv) Diborane reacts with ammonia to give borazine at 450 K. 
B
2
H
6
  + 6NH
3
   ? 3B
3
N
3
H
6
   + 12H
2
 
• Borazine has a cyclic structure similar to benzene and thus is  called inorganic 
benzene 
• The other elements of this group form only a few stable hydrides. The thermal 
stability decreases as we move down the group. 
Page 5


133 
 
CHAPTER 11 
The p-block elements 
Elements in which the last electron enters in the any one of the three p- orbital of 
their outermost shells – p-block elements 
•
 Gen. electronic configuration of outer shell is  ns
2
np
1-6 
The inner core of e-config.may differ which greatly influences their physical & to 
some extent chemical properties. 
• The block of elements in the periodic table consisting of the main groups : 
• Group 13         (B to Tl) 
• Group14        (C to Pb) 
•  Group15         (N to Bi)  
• Group 16         (O to Po) 
• Group17        (F to At) 
• Group18   (He to Rn) 
(1)   Members at the top and on the right of the p-block are nonmetals (C, N,   P, O, 
F, S, Cl, Br, I, At).  
(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).  
(3)    Between the two, from the top left to bottom right, lie an ill-defined group of 
metalloid elements (B, Si, Ge, As, Te) 
GROUP 13  :  The boron group 
 Outer Electronic Configuration:-ns
2
np
1
 
• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& 
thallium (Tl) .             All, except boron, are metals. 
• Boron show diagonal relationship with Silicon;  both are semiconductors 
metalloids & forms covalent compounds. 
•  Boron compounds are electron deficient, they are lack of an octet of electrons 
about the B atom . 
• diborane  B
2
H
6
, is  simplest boron hydride 
134 
 
• Structure: three-center two-electron: the H atoms are simultaneously bonded to 
two B atoms the B-H bridging bond lengths are greater than B-H terminal. 
• - Boron oxide is acidic (it reacts readily with water to form boric acid) 
• aluminium compounds:aluminium oxide is amphoteric  
• aluminum halides, e.g., AlCl
3
 is dimer, an important catalyst in organic 
chemistry have anincomplete octet, acts as Lewic acid by accepting lone pairs 
from Lewic bases, forming adduct 
• aluminum hydride, e.g., LiAlH
4
, a reducing agent 
• Atomic Properties - Electronic Configurations 
Element Symbol Atomic 
No. 
Electronic 
Configuration 
Abundance in Earth’s 
Crest (in ppm) 
Boron B 5 [He]2s
2
 2p
1
 8 
Aluminium Al 13 [Ne]3s
2
 3p
1
 81,300 
Galium Ga 31 [Ar]3d
10
4s
2
 4p
1
 15 
Indium In 49 [Kr] 4d
10
5s
2
 5p
1
 1 
Thallium Tl 81 [Xe] 5d
10
6s
2
 6p
1
 0.3 
 
. Atomic and ionic radii 
• The atomic and ionic radii of group 13 elements are compared to 
corresponding elements of group 2.   From left to right in the period, the 
magnitude of nuclear charge increases but the electrons are added to, the same 
shell.  These electrons do not screen each other, therefore, the electrons 
experience greater nuclear charge. 
•  In other words, effective nuclear charge increases and thus, size decreases. 
Therefore, the elements of this group have smaller size than the corresponding 
elements of second group. 
• On moving down the group both atomic and ionic radii are expected to 
increase due to the addition of new shells. However, the observed atomic 
radius of Al (143 pm) is slightly more than that of Ga (l35 pm). 
Ionization energies 
The first ionization energies of group 13 elements are less than the corresponding 
members of the alkaline earths.  
135 
 
The sharp decrease in I.E. from B to Al is due to increase in size. In case of Ga, there 
are ten d-electrons in its inner electronic configuration.  
The very high value of 3
rd
 I. E. of thallium indicates that +3 O.N. state is not stable, 
rather +1 is more stable for thallium . 
Electropositive (or metallic) character 
the elements of group 13 are less electropositive as compared to elements of group 2. 
On moving down the group the electropositive (metallic) character increases because 
ionization energy decreases. For e.g., Boron is a non-metal white the other elements 
are typical metals.  
Oxidation states 
The common oxidation states of group 13 elements are +3 and + l .The stability of 
the + 1 oxidation state increases in the sequence Al <Ga< In <Tl, Due to Inert pair 
effect. 
        
 
 
Chemical reactivity of Gr.13 Elements 
All elements in their compounds exhibit the oxidation state of + 3 and +1. 
Hydrides 
• None of the group 13 elements reacts directly with hydrogen. However, a no. 
of hydrides of these elements have been prepared by indirect methods. The 
boron hydrides are called boranes& classified in two series:   (a)         B
n
H
n+4
 
called nidoboranes             (b)       B
n
H
n+6
 called arachnoboranes 
• INUDUSTRIAL PREPERATION :- 
2BF
3
(g) + 6LiH(s) ? B
2
H
6
(g)  + 6LiF(s) 
• Laboratory method: 
(i) By the reaction of iodine with sodium borohydride in a high boiling 
solvent.    
2NaBH
4  
+ I
2
  ? B
2
H
6
  + 2NaI    + H
2
   
(ii) By reduction of BCl
3
 with LiAlH
4  
        
4BCl
3
  +  3LiAlH
4  
? 2 B
2
H
6 
 + 3AlCl
3
  + 3 LiCl 
Element B Al Ga In Tl 
Oxidation state +3 +3 +3, +1 +3, +1 +3, +1 
 
136 
 
                                                       
Structure of Diborane, B
2
H
6 
 
 
Some important characteristics of boranes: 
 i) Lower boranes are colourless gases while higher boranes are volatile liquids 
or solids. 
           ii) They undergo spontaneous combustion in air due to strong affinity of boron      
                for oxygen. 
           B
2
H
6
  + 3O
2
  ? B
2
O
3
  + 3H
2
O + Heat 
    iii) Boranes react with alkali metal hydrides in diethyl ether to form    
borohydride complexes.  
      B
2
H
6
  + 2MH ?2M
+
[BH
4
]
-
  (M= Li or Na) 
                              Metal borohydride 
• (iv) Diborane reacts with ammonia to give borazine at 450 K. 
B
2
H
6
  + 6NH
3
   ? 3B
3
N
3
H
6
   + 12H
2
 
• Borazine has a cyclic structure similar to benzene and thus is  called inorganic 
benzene 
• The other elements of this group form only a few stable hydrides. The thermal 
stability decreases as we move down the group. 
137 
 
• AlH
3
 is a colourless solid polymerized via Al - H - Al bridging units. These 
hydrides are weak Lewis acids and readily form adducts with strong Lewis 
base (B:) to give compounds of the type MH
3 
(M = Al or Ga). They also form 
complex-tetrahydrido anions, [MH4]-. The most important tetrahydrido 
compound is  Li[AlH
4
]   
                                            ether 
                 4LiH  + AlCl
3 
????  LiAlH
4
   + 3LiCl 
 
       OXIDES & HYDROXIDES 
• M
2
O
3
&  M(OH)
3
 
 
HALIDES: Structure of boron trihalides 
 
Dimeric structure of aluminium chloride 
– Boron halides do not form dimers because the size of boron 
is so small that it is unable to coordinate four large-sized 
halide ions. 
 
 Anomalous properties of boron 
1. Boron is a non-metal & bad conductor of electricity whereas aluminium is a metal 
& good conductor. B is  hard but  Al is a soft metal.  
2.  Boron exists in two forms-crystalline and amorphous. But Al does not exist in 
different forms.