Chapter 7 - p-Block Elements - Lecture Notes, Chemistry, Class XII - Class 12 PDF Download

 Page 1


7. p-Block Elements 
Points to remember:- 
The general valence shell electronic configuration of p-block elements ns
2
 np
1-6 
 
GROUP 15 ELEMENTS:- 
Group 15 elements ; N, P, As, Sb & Bi 
General electronic configuration: ns
2
np
3
 
Physical Properties:- 
? Dinitrogen is a diatomic gas while all others are solids. 
? N & P are non-metals. As & Sb metalloids & Bi is a metals . this is due to decrease in ionization 
enthalpy & increase in atomic size . 
? Electro negativity decreases down the  group . 
Chemical properties:- 
o Common oxidation states : -3, +3 & +5. 
o Due to inert effect, the stability of +5 state decreases down the group & stability of +3 state 
increases . 
o In the case of Nitrogen all Oxidation states from +1 to +4 tend to disproportionate in acid 
solution , e.g.:- 3HNO 3?H 2O +2NO 
Anamalous  behavior of Nitrogen :- due to its small size, high electronegativity, high ionization 
enthalpy and absence of d-orbital. 
 
N 2 has unique ability to pp-pp multiple bonds whereas the heavier of this group do not form   pp 
–pp because there atomic orbitals are so large & diffuse that they cannot have effective 
overlapping.  
Nitrogen exists as diatomic molecule with triple bond between the two atoms whereas other 
elements form single bonds in elemental state. 
N cannot form dp-pp due to the non availibility of d-orbitals whereas other elements can. 
Trends In Properties:- 
Stability  - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Bond Dissociation Enthalpy- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Reducing character - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Basic character- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Acidic character- N 2O 3>P 2O 3>As 2O 3>Sb 2O 3>Bi 2O 3 
Dinitrogen:- 
Preparation 
? Commercial preparation – By the liquification & fractional distillation of air. 
? Laboratory preparation – By treating an aqueous solution NH 4Cl with sodium nitrate . 
NH 4Cl +NaNO 2?N 2 + 2H 2O + NaCl  
Page 2


7. p-Block Elements 
Points to remember:- 
The general valence shell electronic configuration of p-block elements ns
2
 np
1-6 
 
GROUP 15 ELEMENTS:- 
Group 15 elements ; N, P, As, Sb & Bi 
General electronic configuration: ns
2
np
3
 
Physical Properties:- 
? Dinitrogen is a diatomic gas while all others are solids. 
? N & P are non-metals. As & Sb metalloids & Bi is a metals . this is due to decrease in ionization 
enthalpy & increase in atomic size . 
? Electro negativity decreases down the  group . 
Chemical properties:- 
o Common oxidation states : -3, +3 & +5. 
o Due to inert effect, the stability of +5 state decreases down the group & stability of +3 state 
increases . 
o In the case of Nitrogen all Oxidation states from +1 to +4 tend to disproportionate in acid 
solution , e.g.:- 3HNO 3?H 2O +2NO 
Anamalous  behavior of Nitrogen :- due to its small size, high electronegativity, high ionization 
enthalpy and absence of d-orbital. 
 
N 2 has unique ability to pp-pp multiple bonds whereas the heavier of this group do not form   pp 
–pp because there atomic orbitals are so large & diffuse that they cannot have effective 
overlapping.  
Nitrogen exists as diatomic molecule with triple bond between the two atoms whereas other 
elements form single bonds in elemental state. 
N cannot form dp-pp due to the non availibility of d-orbitals whereas other elements can. 
Trends In Properties:- 
Stability  - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Bond Dissociation Enthalpy- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Reducing character - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Basic character- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Acidic character- N 2O 3>P 2O 3>As 2O 3>Sb 2O 3>Bi 2O 3 
Dinitrogen:- 
Preparation 
? Commercial preparation – By the liquification & fractional distillation of air. 
? Laboratory preparation – By treating an aqueous solution NH 4Cl with sodium nitrate . 
NH 4Cl +NaNO 2?N 2 + 2H 2O + NaCl  
? Thermal decomposition of ammonium dichromate olso gise N 2. 
(NH 4) 2Cr 2O 7? N 2 +4H 2O + Cr 2O 3 
? Thermal decomposition of Barium or Sodium azide gives very pure N 2. 
PROPERTIES  
At high temperature nitrogen combines with metals to form ionic nitride (Mg 3N 2) & with non-
metals , covalent nitride. 
AMMONIA PREPARATION 
? In laboratory it is prepared by heating ammonium salt with NaOH or lime. 
2NH 4Cl + Ca(OH) 2?2NH 3+2H 2O + CaCl 2 
? In large scale it is manufactured by Haber ’process 
N 2+3H 2=2NH 3 
?H
0
= -46.1kJ/mol 
Acc.to Lechatelier’s principle the favourable conditions for the manufacture of NH 3 
are:- 
Optimum temperature : 700 K  
High pressure : 200 atm                                                         
      Catalytst: Iron Oxides 
Promoter : K 2O & Al 2O 3 
PROPERTIES  
Ammonia is a colorless gas with pungent odour. 
Highly soluble in water. 
In solids & liquid states it exists as an associated molecule due to hydrogen bonding witch accounts for 
high melting & boiling points of NH 3 
Trigonal Pyramidal shape NH 3 molecule. 
Aqueous solution of ammonia is weakly basic due to the formation of OH
-
 ion . 
ZnSO 4+ 2NH 4OH?Zn(OH) 2+ (NH 4) 2SO 4 
Ammonia can form coordinate bonds by donating its lone on nitrogen, ammonia forms complexes. 
CuSO 4+4NH 3?[Cu(NH 3) 4] 2SO 4 
Name Formula Oxidation state  Chemical nature  
Nitrous oxide or 
Laughing gas  
N 2O +1 Neutral 
Page 3


7. p-Block Elements 
Points to remember:- 
The general valence shell electronic configuration of p-block elements ns
2
 np
1-6 
 
GROUP 15 ELEMENTS:- 
Group 15 elements ; N, P, As, Sb & Bi 
General electronic configuration: ns
2
np
3
 
Physical Properties:- 
? Dinitrogen is a diatomic gas while all others are solids. 
? N & P are non-metals. As & Sb metalloids & Bi is a metals . this is due to decrease in ionization 
enthalpy & increase in atomic size . 
? Electro negativity decreases down the  group . 
Chemical properties:- 
o Common oxidation states : -3, +3 & +5. 
o Due to inert effect, the stability of +5 state decreases down the group & stability of +3 state 
increases . 
o In the case of Nitrogen all Oxidation states from +1 to +4 tend to disproportionate in acid 
solution , e.g.:- 3HNO 3?H 2O +2NO 
Anamalous  behavior of Nitrogen :- due to its small size, high electronegativity, high ionization 
enthalpy and absence of d-orbital. 
 
N 2 has unique ability to pp-pp multiple bonds whereas the heavier of this group do not form   pp 
–pp because there atomic orbitals are so large & diffuse that they cannot have effective 
overlapping.  
Nitrogen exists as diatomic molecule with triple bond between the two atoms whereas other 
elements form single bonds in elemental state. 
N cannot form dp-pp due to the non availibility of d-orbitals whereas other elements can. 
Trends In Properties:- 
Stability  - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Bond Dissociation Enthalpy- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Reducing character - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Basic character- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Acidic character- N 2O 3>P 2O 3>As 2O 3>Sb 2O 3>Bi 2O 3 
Dinitrogen:- 
Preparation 
? Commercial preparation – By the liquification & fractional distillation of air. 
? Laboratory preparation – By treating an aqueous solution NH 4Cl with sodium nitrate . 
NH 4Cl +NaNO 2?N 2 + 2H 2O + NaCl  
? Thermal decomposition of ammonium dichromate olso gise N 2. 
(NH 4) 2Cr 2O 7? N 2 +4H 2O + Cr 2O 3 
? Thermal decomposition of Barium or Sodium azide gives very pure N 2. 
PROPERTIES  
At high temperature nitrogen combines with metals to form ionic nitride (Mg 3N 2) & with non-
metals , covalent nitride. 
AMMONIA PREPARATION 
? In laboratory it is prepared by heating ammonium salt with NaOH or lime. 
2NH 4Cl + Ca(OH) 2?2NH 3+2H 2O + CaCl 2 
? In large scale it is manufactured by Haber ’process 
N 2+3H 2=2NH 3 
?H
0
= -46.1kJ/mol 
Acc.to Lechatelier’s principle the favourable conditions for the manufacture of NH 3 
are:- 
Optimum temperature : 700 K  
High pressure : 200 atm                                                         
      Catalytst: Iron Oxides 
Promoter : K 2O & Al 2O 3 
PROPERTIES  
Ammonia is a colorless gas with pungent odour. 
Highly soluble in water. 
In solids & liquid states it exists as an associated molecule due to hydrogen bonding witch accounts for 
high melting & boiling points of NH 3 
Trigonal Pyramidal shape NH 3 molecule. 
Aqueous solution of ammonia is weakly basic due to the formation of OH
-
 ion . 
ZnSO 4+ 2NH 4OH?Zn(OH) 2+ (NH 4) 2SO 4 
Ammonia can form coordinate bonds by donating its lone on nitrogen, ammonia forms complexes. 
CuSO 4+4NH 3?[Cu(NH 3) 4] 2SO 4 
Name Formula Oxidation state  Chemical nature  
Nitrous oxide or 
Laughing gas  
N 2O +1 Neutral 
Nitric oxide NO +2 Neutral 
Dinitrogen trioxide  N 2O 3 +3 Acidic 
Dinitrogen tetra oxide N 2O 4or NO 2 +4 Acidic 
Dinitrogen pentaoxide N 2O 5 +5 Acidic 
NITRIC ACID 
PREPARATION:ostwald’s procees – it is based upon catalytic oxidation of ammonia by atmospheric 
oxidation . The main steps are  
1)   4NH 3 + 5O 2
-PT
500K, 9BAR
--
? 4NO + 6H 2O 
2)    2NO+O 2?2HNO 3+ NO 
PROPERTIES:- 
(i)conc. HNO 3 is a strong oxidizing agent & attacks most metals gold & Pt. .  
       (ii)Cr & Al do not dissolve HNO 3 because of the formation of a positive film of oxide on the surface. 
      (iii)it oxidises non metals like I 2 to HNO 3, C to CO 2 , S to H 2so 4 
      (iv)brown ring tes is used to detect NO
-
. 
PHOSPHOROUS:- 
ALLOTROPIC FORMS: White , red a-black &ß-black . 
White phosphorous is more reactive red phosphorous because white P exists as discrete P 4 molecules . 
in red P several P 4molecules are linked to formed polymeric chain. 
 
PHOSPHINE 
Preparation:It is prepared in laboratory by heating white P with concentrated naoh solution in an 
Inert atmosphere of CO 2 [P 4+3NaOH+3H 2O ?  PH 3+3NaH 2PO 2] 
Phosphorous halides 
Phosphorous forms two types of halides PX 3& PX 5 (X=F,I,Br) 
Trihalides have pyramidal shape and pentahalides have trigonal bipyramidal structure. 
OXOACIDS OF PHOSPHOROUS 
? The acids in +3 oxidation state disproportionate to higher & lower oxidation. 
4H 3PO 3 ? 3H 3PO 4+PH 3 
Page 4


7. p-Block Elements 
Points to remember:- 
The general valence shell electronic configuration of p-block elements ns
2
 np
1-6 
 
GROUP 15 ELEMENTS:- 
Group 15 elements ; N, P, As, Sb & Bi 
General electronic configuration: ns
2
np
3
 
Physical Properties:- 
? Dinitrogen is a diatomic gas while all others are solids. 
? N & P are non-metals. As & Sb metalloids & Bi is a metals . this is due to decrease in ionization 
enthalpy & increase in atomic size . 
? Electro negativity decreases down the  group . 
Chemical properties:- 
o Common oxidation states : -3, +3 & +5. 
o Due to inert effect, the stability of +5 state decreases down the group & stability of +3 state 
increases . 
o In the case of Nitrogen all Oxidation states from +1 to +4 tend to disproportionate in acid 
solution , e.g.:- 3HNO 3?H 2O +2NO 
Anamalous  behavior of Nitrogen :- due to its small size, high electronegativity, high ionization 
enthalpy and absence of d-orbital. 
 
N 2 has unique ability to pp-pp multiple bonds whereas the heavier of this group do not form   pp 
–pp because there atomic orbitals are so large & diffuse that they cannot have effective 
overlapping.  
Nitrogen exists as diatomic molecule with triple bond between the two atoms whereas other 
elements form single bonds in elemental state. 
N cannot form dp-pp due to the non availibility of d-orbitals whereas other elements can. 
Trends In Properties:- 
Stability  - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Bond Dissociation Enthalpy- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Reducing character - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Basic character- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Acidic character- N 2O 3>P 2O 3>As 2O 3>Sb 2O 3>Bi 2O 3 
Dinitrogen:- 
Preparation 
? Commercial preparation – By the liquification & fractional distillation of air. 
? Laboratory preparation – By treating an aqueous solution NH 4Cl with sodium nitrate . 
NH 4Cl +NaNO 2?N 2 + 2H 2O + NaCl  
? Thermal decomposition of ammonium dichromate olso gise N 2. 
(NH 4) 2Cr 2O 7? N 2 +4H 2O + Cr 2O 3 
? Thermal decomposition of Barium or Sodium azide gives very pure N 2. 
PROPERTIES  
At high temperature nitrogen combines with metals to form ionic nitride (Mg 3N 2) & with non-
metals , covalent nitride. 
AMMONIA PREPARATION 
? In laboratory it is prepared by heating ammonium salt with NaOH or lime. 
2NH 4Cl + Ca(OH) 2?2NH 3+2H 2O + CaCl 2 
? In large scale it is manufactured by Haber ’process 
N 2+3H 2=2NH 3 
?H
0
= -46.1kJ/mol 
Acc.to Lechatelier’s principle the favourable conditions for the manufacture of NH 3 
are:- 
Optimum temperature : 700 K  
High pressure : 200 atm                                                         
      Catalytst: Iron Oxides 
Promoter : K 2O & Al 2O 3 
PROPERTIES  
Ammonia is a colorless gas with pungent odour. 
Highly soluble in water. 
In solids & liquid states it exists as an associated molecule due to hydrogen bonding witch accounts for 
high melting & boiling points of NH 3 
Trigonal Pyramidal shape NH 3 molecule. 
Aqueous solution of ammonia is weakly basic due to the formation of OH
-
 ion . 
ZnSO 4+ 2NH 4OH?Zn(OH) 2+ (NH 4) 2SO 4 
Ammonia can form coordinate bonds by donating its lone on nitrogen, ammonia forms complexes. 
CuSO 4+4NH 3?[Cu(NH 3) 4] 2SO 4 
Name Formula Oxidation state  Chemical nature  
Nitrous oxide or 
Laughing gas  
N 2O +1 Neutral 
Nitric oxide NO +2 Neutral 
Dinitrogen trioxide  N 2O 3 +3 Acidic 
Dinitrogen tetra oxide N 2O 4or NO 2 +4 Acidic 
Dinitrogen pentaoxide N 2O 5 +5 Acidic 
NITRIC ACID 
PREPARATION:ostwald’s procees – it is based upon catalytic oxidation of ammonia by atmospheric 
oxidation . The main steps are  
1)   4NH 3 + 5O 2
-PT
500K, 9BAR
--
? 4NO + 6H 2O 
2)    2NO+O 2?2HNO 3+ NO 
PROPERTIES:- 
(i)conc. HNO 3 is a strong oxidizing agent & attacks most metals gold & Pt. .  
       (ii)Cr & Al do not dissolve HNO 3 because of the formation of a positive film of oxide on the surface. 
      (iii)it oxidises non metals like I 2 to HNO 3, C to CO 2 , S to H 2so 4 
      (iv)brown ring tes is used to detect NO
-
. 
PHOSPHOROUS:- 
ALLOTROPIC FORMS: White , red a-black &ß-black . 
White phosphorous is more reactive red phosphorous because white P exists as discrete P 4 molecules . 
in red P several P 4molecules are linked to formed polymeric chain. 
 
PHOSPHINE 
Preparation:It is prepared in laboratory by heating white P with concentrated naoh solution in an 
Inert atmosphere of CO 2 [P 4+3NaOH+3H 2O ?  PH 3+3NaH 2PO 2] 
Phosphorous halides 
Phosphorous forms two types of halides PX 3& PX 5 (X=F,I,Br) 
Trihalides have pyramidal shape and pentahalides have trigonal bipyramidal structure. 
OXOACIDS OF PHOSPHOROUS 
? The acids in +3 oxidation state disproportionate to higher & lower oxidation. 
4H 3PO 3 ? 3H 3PO 4+PH 3 
? Acids which contains P-H bond have strong reducing properties.EX:-H 3PO 2 
Are ionisable and cause the basicity. 
? Hydrogen atom which are attached with oxygen in P-OH form are ionisable 
 
GROUP-16 ELEMENTS (CHALCOGENS) 
Grouo 16 Elements:O,S,SE,TE,PO 
General electronic configuration:ns
2
np
4 
 
Element Occurence 
 
 
Oxygen Comprises 20.946% by volume of the atmosphere. 
 
Sulphur As sulphates such as gypsum CaSO 4.2H 2O,Epsom salt MgSO 4.7H 2O and sulphides 
 Such as galena PbS,zinc blende ZnS,copper pyrites CuFeS 2 
 
 As metal selenides and tellurides in sulphide ores. 
 
 
Se&Te as a decay product of thorium and uranium minerals. 
 
ATOMIC & PHYSICAL PROPERTIES 
 
? Ionisation enthalpy decreases from oxygen to polonium. 
? Oxygen atom has less negative electron gain enthalpy than S because of the compact 
nature of the oxygen atom.However from the S onwards the value again becomes less 
negative upto polonium. 
? Electronegativity gradually decreases from oxygen to polonium,metallic character 
increases from oxygen to polonium. 
? Oxygen & S are non-metals,selenium and telerium are metalloids.Po is a radioactive 
metal. 
? Oxygen is a diatomic gas while S,Se&Te are octa atomic S 8,Se 8&Te 8 molecules which has 
puckered ’ ring’ structure. 
Page 5


7. p-Block Elements 
Points to remember:- 
The general valence shell electronic configuration of p-block elements ns
2
 np
1-6 
 
GROUP 15 ELEMENTS:- 
Group 15 elements ; N, P, As, Sb & Bi 
General electronic configuration: ns
2
np
3
 
Physical Properties:- 
? Dinitrogen is a diatomic gas while all others are solids. 
? N & P are non-metals. As & Sb metalloids & Bi is a metals . this is due to decrease in ionization 
enthalpy & increase in atomic size . 
? Electro negativity decreases down the  group . 
Chemical properties:- 
o Common oxidation states : -3, +3 & +5. 
o Due to inert effect, the stability of +5 state decreases down the group & stability of +3 state 
increases . 
o In the case of Nitrogen all Oxidation states from +1 to +4 tend to disproportionate in acid 
solution , e.g.:- 3HNO 3?H 2O +2NO 
Anamalous  behavior of Nitrogen :- due to its small size, high electronegativity, high ionization 
enthalpy and absence of d-orbital. 
 
N 2 has unique ability to pp-pp multiple bonds whereas the heavier of this group do not form   pp 
–pp because there atomic orbitals are so large & diffuse that they cannot have effective 
overlapping.  
Nitrogen exists as diatomic molecule with triple bond between the two atoms whereas other 
elements form single bonds in elemental state. 
N cannot form dp-pp due to the non availibility of d-orbitals whereas other elements can. 
Trends In Properties:- 
Stability  - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Bond Dissociation Enthalpy- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Reducing character - NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Basic character- NH 3>PH 3>AsH 3>SbH 3>BiH 3 
Acidic character- N 2O 3>P 2O 3>As 2O 3>Sb 2O 3>Bi 2O 3 
Dinitrogen:- 
Preparation 
? Commercial preparation – By the liquification & fractional distillation of air. 
? Laboratory preparation – By treating an aqueous solution NH 4Cl with sodium nitrate . 
NH 4Cl +NaNO 2?N 2 + 2H 2O + NaCl  
? Thermal decomposition of ammonium dichromate olso gise N 2. 
(NH 4) 2Cr 2O 7? N 2 +4H 2O + Cr 2O 3 
? Thermal decomposition of Barium or Sodium azide gives very pure N 2. 
PROPERTIES  
At high temperature nitrogen combines with metals to form ionic nitride (Mg 3N 2) & with non-
metals , covalent nitride. 
AMMONIA PREPARATION 
? In laboratory it is prepared by heating ammonium salt with NaOH or lime. 
2NH 4Cl + Ca(OH) 2?2NH 3+2H 2O + CaCl 2 
? In large scale it is manufactured by Haber ’process 
N 2+3H 2=2NH 3 
?H
0
= -46.1kJ/mol 
Acc.to Lechatelier’s principle the favourable conditions for the manufacture of NH 3 
are:- 
Optimum temperature : 700 K  
High pressure : 200 atm                                                         
      Catalytst: Iron Oxides 
Promoter : K 2O & Al 2O 3 
PROPERTIES  
Ammonia is a colorless gas with pungent odour. 
Highly soluble in water. 
In solids & liquid states it exists as an associated molecule due to hydrogen bonding witch accounts for 
high melting & boiling points of NH 3 
Trigonal Pyramidal shape NH 3 molecule. 
Aqueous solution of ammonia is weakly basic due to the formation of OH
-
 ion . 
ZnSO 4+ 2NH 4OH?Zn(OH) 2+ (NH 4) 2SO 4 
Ammonia can form coordinate bonds by donating its lone on nitrogen, ammonia forms complexes. 
CuSO 4+4NH 3?[Cu(NH 3) 4] 2SO 4 
Name Formula Oxidation state  Chemical nature  
Nitrous oxide or 
Laughing gas  
N 2O +1 Neutral 
Nitric oxide NO +2 Neutral 
Dinitrogen trioxide  N 2O 3 +3 Acidic 
Dinitrogen tetra oxide N 2O 4or NO 2 +4 Acidic 
Dinitrogen pentaoxide N 2O 5 +5 Acidic 
NITRIC ACID 
PREPARATION:ostwald’s procees – it is based upon catalytic oxidation of ammonia by atmospheric 
oxidation . The main steps are  
1)   4NH 3 + 5O 2
-PT
500K, 9BAR
--
? 4NO + 6H 2O 
2)    2NO+O 2?2HNO 3+ NO 
PROPERTIES:- 
(i)conc. HNO 3 is a strong oxidizing agent & attacks most metals gold & Pt. .  
       (ii)Cr & Al do not dissolve HNO 3 because of the formation of a positive film of oxide on the surface. 
      (iii)it oxidises non metals like I 2 to HNO 3, C to CO 2 , S to H 2so 4 
      (iv)brown ring tes is used to detect NO
-
. 
PHOSPHOROUS:- 
ALLOTROPIC FORMS: White , red a-black &ß-black . 
White phosphorous is more reactive red phosphorous because white P exists as discrete P 4 molecules . 
in red P several P 4molecules are linked to formed polymeric chain. 
 
PHOSPHINE 
Preparation:It is prepared in laboratory by heating white P with concentrated naoh solution in an 
Inert atmosphere of CO 2 [P 4+3NaOH+3H 2O ?  PH 3+3NaH 2PO 2] 
Phosphorous halides 
Phosphorous forms two types of halides PX 3& PX 5 (X=F,I,Br) 
Trihalides have pyramidal shape and pentahalides have trigonal bipyramidal structure. 
OXOACIDS OF PHOSPHOROUS 
? The acids in +3 oxidation state disproportionate to higher & lower oxidation. 
4H 3PO 3 ? 3H 3PO 4+PH 3 
? Acids which contains P-H bond have strong reducing properties.EX:-H 3PO 2 
Are ionisable and cause the basicity. 
? Hydrogen atom which are attached with oxygen in P-OH form are ionisable 
 
GROUP-16 ELEMENTS (CHALCOGENS) 
Grouo 16 Elements:O,S,SE,TE,PO 
General electronic configuration:ns
2
np
4 
 
Element Occurence 
 
 
Oxygen Comprises 20.946% by volume of the atmosphere. 
 
Sulphur As sulphates such as gypsum CaSO 4.2H 2O,Epsom salt MgSO 4.7H 2O and sulphides 
 Such as galena PbS,zinc blende ZnS,copper pyrites CuFeS 2 
 
 As metal selenides and tellurides in sulphide ores. 
 
 
Se&Te as a decay product of thorium and uranium minerals. 
 
ATOMIC & PHYSICAL PROPERTIES 
 
? Ionisation enthalpy decreases from oxygen to polonium. 
? Oxygen atom has less negative electron gain enthalpy than S because of the compact 
nature of the oxygen atom.However from the S onwards the value again becomes less 
negative upto polonium. 
? Electronegativity gradually decreases from oxygen to polonium,metallic character 
increases from oxygen to polonium. 
? Oxygen & S are non-metals,selenium and telerium are metalloids.Po is a radioactive 
metal. 
? Oxygen is a diatomic gas while S,Se&Te are octa atomic S 8,Se 8&Te 8 molecules which has 
puckered ’ ring’ structure. 
 
CHEMICAL PROPERTIES 
? Common oxidation state:-   -2,+2,+4 &+6. 
? Due to inert effect,the stability of +6  decreases down the group and stability of +4 
increases. 
Oxygen exhibits +1 state in O 2F 2,+2 in OF 2. 
Anamolous behavior of oxygen-due to its small size,high electronegativity and absence of d-
orbitals. 
TREND IN PROPERTIES 
Acidic character-H 2O<H 2S<H 2Se<H 2Te 
Thermal stability-H 2O>H 2S>H 2Se>H 2Te 
Reducing character-H 2S<H 2Se<H 2Te 
Boiling point-H 2S<H 2Se<H 2Te<H 2O 
Reducing property of dioxides-SO 2>SeO 2>TeO 2 
Stability of halides-F>Cl>Br>I 
HALIDES 
DI HALIDES:sp
3
 hybridisation but angular structure. 
TETRA HALIDES:sp3 hybridisation-see-saw geometry 
HEXA HALIDES:sp
3
d
2
,octahedral SF 6 
DIOXYGEN 
Prepared by heating oxygen containing salts like chlorates,nitrares 
     2KClO 3
-heat
---- ? 2KCl+3O 2 
2Fe
3+
+SO 2+2H 2O ?2Fe
2+ 
+ SO 4
2-
 + 4H
+ 
5SO 2+2MnO 4
- 
+2H 2O ?5SO 4
2-
 +4H
+
 +2Mn
2+
 
SO2 molecule is angular. 
OXIDES