DAY TWENTY SIX
p-Block Elements
(Groups 15 to18)
Learning & Revision for the Day
u Group- 15 Elements : Nitrogen Family u Group -17 Elements : Halogens
u Group-16 Elements : Oxygen Family u Group- 18 Elements : Noble Gases
Group-15 Elements : Nitrogen Family
Group 15th elements are nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and
bismuth (Bi). Nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids
and bismuth is a typical metal.
Occurrence
Occurrence of the Group-15 elements are given in the following table:
Occurrence/ore and Abundance of Group VA Elements
Element Abundance by weight (ppm) Occurrence/Ore
N 19 (33rd most abundant) Chile saltpetre -NaNO 3, saltpetre -KNO 3
P 1120 (11th most abundant) Phosphorite Ca 3(PO 4 ) 2, Fluorapatite Ca 5(PO 4 ) 3F or
3 [Ca 3(PO 4 ) 2 ] ⋅ CaF2,
Hydroxyapatite -Ca 5 (PO 4 ) 3OH
or 3 Ca 3(PO 4 ) 2 ⋅ Ca(OH) 2, chlorapatite Ca 5(PO 4 ) 3Cl
or 3 [Ca 3(PO 4 ) 2 ] ⋅ CaCl 2.
As 1.8 (52nd most abundant) Arsenopyrite -FeAsS, Realgar α - As 4S 4 , Orpiment
- As 2S 3, Arsenides such as NiAs, NiAs 2, FeAs 2
Sb 0.20 (64th most abundant) Stibnite -Sb 2S 3
Bi 0.008 (71st most abundant) Bismuthinite - , Bismite - Bi 2O 3
,Trends in Physical and Property Down the group Reason
Reducing Increases As the stability of hydrides
Chemical Properties character decreases the reducing
Some important physical and chemical properties of group-15 character increases.
elements are as follows ; Melting and Increases NH 3 has higher melting point
boiling point (except in N) and boiling point than PH 3 due
Electronic Configuration to hydrogen bonding. As the
molecular size increases van
l The general electronic configuration of various elements of
der Waals’ forces increases.
group 15 is ns2 np3 .
l Atomic and ionic radius increases down the group, l Elements of group VA form two types of halides, trihalides
however arsenic shows exceptionally low value of atomic and pentahalides.
volume. l Trihalides are mainly basic (Lewis bases) in nature and
l Ionisation energy of these elements is much higher due to have lone pair of electrons (central atom is sp3 -hybridised)
increased nuclear charge and stable exactly half-filled with pyramidal shape.
electronic configuration. l Pentahalides are sp3d-hybridised and trigonal bipyramidal
l On moving down the group electronegativity decreases due in shape.
to gradual increase in the atomic radius of the elements. Properties of Halides
l On moving down the group, metallic character increases.
Property Gradation Reason
l All these elements show allotropy (except bismuth). Stability of NF3 > NCl 3 > NBr3 Large size difference
trihalides of between N and the
Oxidation States nitrogen halogens
l Elements of group VA exhibit maximum oxidation state of Lewis base NF3 < NCl 3 < NBr3 Decreasing
+ 5 by losing all the five electrons in their outer most shell. strength < NI 3 electronegativity of
+ 3 oxidation state is shown when only p-orbital electrons halogens.
are used in bonding or (–) 3 by using 3 electrons with less
Bond angle PF3 < PCl 3 < PBr3 Due to decreased bond
electronegative elements.
among the halides < PI 3 pair-bond pair repulsion as
l On moving down, + 3 oxidation state becomes more stable of phosphorus these move away from P.
due to inert pair effect. Nitrogen shows +5 to −3 oxidation
states. l All the elements of group VA form two types of oxides, i.e.
M2 O3 and M2 O 5 and are called trioxides and pentaoxides.
l General formula of hydrides of these elements is MH3 , e.g.
NH3 , PH3 , AsH3 , SbH3 and BiH3 . Properties of Oxides
Property Gradation Reason
Acidic strength of N 2O 3 > P2O 3 > As 2O 3 Electronegativity of
P N trioxides central atom decreases
H Acidic strength of N 2O 5 > P2O 5 > As 2O 5 Electronegativity of
93.6° H H 107° H
pentaoxides > Sb 2O 5 > Bi 2O 5 central atom decreases
H H
Acidic strength of N 2O < NO < N 2O 3 Oxidation state of
All these hydrides are covalent in nature and have pyramidal
oxides of nitrogen < N 2O 4 < N 2O 5 central atom increases
structure (sp3 -hybridised).
Stability of P2O 5 > As 2O 5 > Sb 2O 5 Stability of oxides of a
Properties of Hydrides pentaoxides > N 2O 5 higher oxidation state, i.e.
M 2O 5 decreases with
Property Down the group Reason increasing atomic
Bond angle of Decreases As the size of central atom number due to inert pair
MH 3 increases, electronegativity effect
decreases, thus repulsion of
bond pair and lone pair of
central atom decreases. Dinitrogen (N 2 )
Basic strength Decreases As the size of central atom Preparation
of MH 3 increases, electron density
decreases. NH4Cl(aq ) + NaNO2 (aq ) → N2(g) + 2H2O(l ) + NaCl (aq )
Heat
Thermal Decreases As the size of the central atom (NH4 )2 Cr2O7 → N2 + 4H2O + Cr2O3
stability of increases, its tendency to form Ba(N3 )2 → Ba + 3N2
MH 3 stable M—H bond decreases.
, Properties Cu2 + (aq ) + 4 NH3 (aq ) q [Cu(NH3 )4 ]2+ (aq )
Blue D eep blue .
l Nitrogen does not react with alkali metals except Li but
−
reacts with alkaline earth metals to give metal nitride. Ag (aq )+ Cl (aq ) → AgCl(s)
+
Colourless White ppt.
Heat
6 Li + N2 → 2Li3 N
AgCl (s) + 2NH3 (aq ) → [Ag(NH3 )2 ] Cl(aq )
Heat
3Mg + N2 → Mg3 N2 White ppt. Colourless
2000 K l NH3 is used in refrigeration due to its large
l N2(g) + O2 (g) → 2 NO(g) heat of evaporation and in manufacture of HNO3 , NaHCO3 ,
Heat ammonium compounds and nitrogenous fertilizers.
l 2B + N2 → 2BN
l
1273 K
CaC2 + N2 → CaCN2 + C 2. Nitric Acid (HNO3 )
It was earlier known as aqua fortis. It is prepared by the
Uses following processes.
l Liquid N2 is used as refrigerant. l Laboratory preparation of HNO3 is as follows:
l It is used in the manufacture of HNO3 , NH3 , CaCN2 NaNO3 ( s) + H2SO 4( aq) → NaHSO 4( aq) + HNO3 ( aq)
(calcium cyanamide) and other nitrogenous compounds. l Ostwald process is the commercial process for
l It is used for filling electric bulbs. manufacturing HNO3 .
Pt gauge
Some Important Compounds 4NH3(g) + 5 O2(g) → 4NO(g) + 6 H2O(l ) ; ∆H = − ve
1100 K
of Nitrogen 2 NO(g) + O2 (g) → 2 NO2 (g)
Preparation and properties of nitrogen compounds 3NO2 (g)+ H2O(e) → 2HNO3 (aq ) + NO(g)
are as follows:
l Anhydrous HNO3 is a colourless fuming having pungent
smelling liquid. It acquires yellow colour due to its
1. Ammonia decomposition.
l It is covalent compound. Due to the presence of lone pair of
Sunlight
electrons, N-atom in NH3 is sp3 hybridised. it acquires 4 HNO3 → 4 NO2 + 2H2O + O2
pyramidal shape. l It has corrosive action on skin and causes painful sores.
l It is prepared by the following methods : l It is very strong acid and form salts on reaction with basic
NH2CONH2 + 2 H2O → (NH4 )2 CO3 oxides, carbonates, hydroxides etc.
Urea
q 2 NH3 + H2O + CO2 Na2CO3 + 2 HNO3 → 2 NaNO3 + H2O + CO2
2NH4Cl + Ca(OH)2 → 2NH3 + 2H2O + CaCl2 l It acts as a strong oxidising agent.
(NH4 )2 SO 4 + 2NaOH → 2 NH3 + 2 H2O + Na2SO 4 l Non-metals such as C, S, P and I2 are oxidised to carbonic
On large scale, ammonia is manufactured by acid, sulphuric acid, orthophosphoric acid and iodic acid
respectively.
Haber’s process.
e.g. C + 4 HNO3 → H2CO3 + 4NO2 + H2O
200 atm
N2 (g) + 3 H2 (g) 2NH3 ; ∆H °f = − 46.1 kJ / mol S + 6 HNO3 → H2SO 4 + 6 NO2 + 2 H2O
723 K; Catalyst l Metalloids such as Sb is oxidised to antimonic acid, As to
Iron oxide is used as catalyst with small amounts of K2O arsenic acid and Sn to stannic acid.
and Al2O3 to increase the rate of attainment of Sb + 5 HNO3 → H3SbO 4 + 5 NO2 + H2O
equilibrium.
As + 5HNO3 → H3 AsO 4 + 5 NO2 + H2O
NH3 is basic in nature, has tendency to form hydrogen
Sn + 4 HNO3 → H2SnO3 + 4 NO2 + H2O
l
bond, therefore soluble in water and form NH4OH or
NH3 (aq ).
l Oxidation of compounds
l Due to basic nature, NH3 is a good complexing agent and 6 FeSO 4 + 3 H2SO 4 + 2 HNO3 →
reducing agent. e.g. 3Fe2 (SO 4 )3 + 2 NO + 4 H2O
2FeCl3 (aq ) + 3NH4OH (aq ) → NO is absorbed by FeSO 4 and a dark brown ring of nitroso
ferrous sulphate is formed (ring test for nitrates).
Fe2O3 ⋅ xH2O(s) + 3 NH4Cl
Brown ppt.
l Metals like iron, cobalt, nickel, chromium, aluminium
ZnSO 4 (aq ) + 2 NH4OH (aq ) → become passive in conc. HNO3 due to the formation of a
Zn(OH)2 (s) + (NH4 )2 SO 4 thin protective film of oxide on the surface of the metal.
White ppt.
p-Block Elements
(Groups 15 to18)
Learning & Revision for the Day
u Group- 15 Elements : Nitrogen Family u Group -17 Elements : Halogens
u Group-16 Elements : Oxygen Family u Group- 18 Elements : Noble Gases
Group-15 Elements : Nitrogen Family
Group 15th elements are nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and
bismuth (Bi). Nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids
and bismuth is a typical metal.
Occurrence
Occurrence of the Group-15 elements are given in the following table:
Occurrence/ore and Abundance of Group VA Elements
Element Abundance by weight (ppm) Occurrence/Ore
N 19 (33rd most abundant) Chile saltpetre -NaNO 3, saltpetre -KNO 3
P 1120 (11th most abundant) Phosphorite Ca 3(PO 4 ) 2, Fluorapatite Ca 5(PO 4 ) 3F or
3 [Ca 3(PO 4 ) 2 ] ⋅ CaF2,
Hydroxyapatite -Ca 5 (PO 4 ) 3OH
or 3 Ca 3(PO 4 ) 2 ⋅ Ca(OH) 2, chlorapatite Ca 5(PO 4 ) 3Cl
or 3 [Ca 3(PO 4 ) 2 ] ⋅ CaCl 2.
As 1.8 (52nd most abundant) Arsenopyrite -FeAsS, Realgar α - As 4S 4 , Orpiment
- As 2S 3, Arsenides such as NiAs, NiAs 2, FeAs 2
Sb 0.20 (64th most abundant) Stibnite -Sb 2S 3
Bi 0.008 (71st most abundant) Bismuthinite - , Bismite - Bi 2O 3
,Trends in Physical and Property Down the group Reason
Reducing Increases As the stability of hydrides
Chemical Properties character decreases the reducing
Some important physical and chemical properties of group-15 character increases.
elements are as follows ; Melting and Increases NH 3 has higher melting point
boiling point (except in N) and boiling point than PH 3 due
Electronic Configuration to hydrogen bonding. As the
molecular size increases van
l The general electronic configuration of various elements of
der Waals’ forces increases.
group 15 is ns2 np3 .
l Atomic and ionic radius increases down the group, l Elements of group VA form two types of halides, trihalides
however arsenic shows exceptionally low value of atomic and pentahalides.
volume. l Trihalides are mainly basic (Lewis bases) in nature and
l Ionisation energy of these elements is much higher due to have lone pair of electrons (central atom is sp3 -hybridised)
increased nuclear charge and stable exactly half-filled with pyramidal shape.
electronic configuration. l Pentahalides are sp3d-hybridised and trigonal bipyramidal
l On moving down the group electronegativity decreases due in shape.
to gradual increase in the atomic radius of the elements. Properties of Halides
l On moving down the group, metallic character increases.
Property Gradation Reason
l All these elements show allotropy (except bismuth). Stability of NF3 > NCl 3 > NBr3 Large size difference
trihalides of between N and the
Oxidation States nitrogen halogens
l Elements of group VA exhibit maximum oxidation state of Lewis base NF3 < NCl 3 < NBr3 Decreasing
+ 5 by losing all the five electrons in their outer most shell. strength < NI 3 electronegativity of
+ 3 oxidation state is shown when only p-orbital electrons halogens.
are used in bonding or (–) 3 by using 3 electrons with less
Bond angle PF3 < PCl 3 < PBr3 Due to decreased bond
electronegative elements.
among the halides < PI 3 pair-bond pair repulsion as
l On moving down, + 3 oxidation state becomes more stable of phosphorus these move away from P.
due to inert pair effect. Nitrogen shows +5 to −3 oxidation
states. l All the elements of group VA form two types of oxides, i.e.
M2 O3 and M2 O 5 and are called trioxides and pentaoxides.
l General formula of hydrides of these elements is MH3 , e.g.
NH3 , PH3 , AsH3 , SbH3 and BiH3 . Properties of Oxides
Property Gradation Reason
Acidic strength of N 2O 3 > P2O 3 > As 2O 3 Electronegativity of
P N trioxides central atom decreases
H Acidic strength of N 2O 5 > P2O 5 > As 2O 5 Electronegativity of
93.6° H H 107° H
pentaoxides > Sb 2O 5 > Bi 2O 5 central atom decreases
H H
Acidic strength of N 2O < NO < N 2O 3 Oxidation state of
All these hydrides are covalent in nature and have pyramidal
oxides of nitrogen < N 2O 4 < N 2O 5 central atom increases
structure (sp3 -hybridised).
Stability of P2O 5 > As 2O 5 > Sb 2O 5 Stability of oxides of a
Properties of Hydrides pentaoxides > N 2O 5 higher oxidation state, i.e.
M 2O 5 decreases with
Property Down the group Reason increasing atomic
Bond angle of Decreases As the size of central atom number due to inert pair
MH 3 increases, electronegativity effect
decreases, thus repulsion of
bond pair and lone pair of
central atom decreases. Dinitrogen (N 2 )
Basic strength Decreases As the size of central atom Preparation
of MH 3 increases, electron density
decreases. NH4Cl(aq ) + NaNO2 (aq ) → N2(g) + 2H2O(l ) + NaCl (aq )
Heat
Thermal Decreases As the size of the central atom (NH4 )2 Cr2O7 → N2 + 4H2O + Cr2O3
stability of increases, its tendency to form Ba(N3 )2 → Ba + 3N2
MH 3 stable M—H bond decreases.
, Properties Cu2 + (aq ) + 4 NH3 (aq ) q [Cu(NH3 )4 ]2+ (aq )
Blue D eep blue .
l Nitrogen does not react with alkali metals except Li but
−
reacts with alkaline earth metals to give metal nitride. Ag (aq )+ Cl (aq ) → AgCl(s)
+
Colourless White ppt.
Heat
6 Li + N2 → 2Li3 N
AgCl (s) + 2NH3 (aq ) → [Ag(NH3 )2 ] Cl(aq )
Heat
3Mg + N2 → Mg3 N2 White ppt. Colourless
2000 K l NH3 is used in refrigeration due to its large
l N2(g) + O2 (g) → 2 NO(g) heat of evaporation and in manufacture of HNO3 , NaHCO3 ,
Heat ammonium compounds and nitrogenous fertilizers.
l 2B + N2 → 2BN
l
1273 K
CaC2 + N2 → CaCN2 + C 2. Nitric Acid (HNO3 )
It was earlier known as aqua fortis. It is prepared by the
Uses following processes.
l Liquid N2 is used as refrigerant. l Laboratory preparation of HNO3 is as follows:
l It is used in the manufacture of HNO3 , NH3 , CaCN2 NaNO3 ( s) + H2SO 4( aq) → NaHSO 4( aq) + HNO3 ( aq)
(calcium cyanamide) and other nitrogenous compounds. l Ostwald process is the commercial process for
l It is used for filling electric bulbs. manufacturing HNO3 .
Pt gauge
Some Important Compounds 4NH3(g) + 5 O2(g) → 4NO(g) + 6 H2O(l ) ; ∆H = − ve
1100 K
of Nitrogen 2 NO(g) + O2 (g) → 2 NO2 (g)
Preparation and properties of nitrogen compounds 3NO2 (g)+ H2O(e) → 2HNO3 (aq ) + NO(g)
are as follows:
l Anhydrous HNO3 is a colourless fuming having pungent
smelling liquid. It acquires yellow colour due to its
1. Ammonia decomposition.
l It is covalent compound. Due to the presence of lone pair of
Sunlight
electrons, N-atom in NH3 is sp3 hybridised. it acquires 4 HNO3 → 4 NO2 + 2H2O + O2
pyramidal shape. l It has corrosive action on skin and causes painful sores.
l It is prepared by the following methods : l It is very strong acid and form salts on reaction with basic
NH2CONH2 + 2 H2O → (NH4 )2 CO3 oxides, carbonates, hydroxides etc.
Urea
q 2 NH3 + H2O + CO2 Na2CO3 + 2 HNO3 → 2 NaNO3 + H2O + CO2
2NH4Cl + Ca(OH)2 → 2NH3 + 2H2O + CaCl2 l It acts as a strong oxidising agent.
(NH4 )2 SO 4 + 2NaOH → 2 NH3 + 2 H2O + Na2SO 4 l Non-metals such as C, S, P and I2 are oxidised to carbonic
On large scale, ammonia is manufactured by acid, sulphuric acid, orthophosphoric acid and iodic acid
respectively.
Haber’s process.
e.g. C + 4 HNO3 → H2CO3 + 4NO2 + H2O
200 atm
N2 (g) + 3 H2 (g) 2NH3 ; ∆H °f = − 46.1 kJ / mol S + 6 HNO3 → H2SO 4 + 6 NO2 + 2 H2O
723 K; Catalyst l Metalloids such as Sb is oxidised to antimonic acid, As to
Iron oxide is used as catalyst with small amounts of K2O arsenic acid and Sn to stannic acid.
and Al2O3 to increase the rate of attainment of Sb + 5 HNO3 → H3SbO 4 + 5 NO2 + H2O
equilibrium.
As + 5HNO3 → H3 AsO 4 + 5 NO2 + H2O
NH3 is basic in nature, has tendency to form hydrogen
Sn + 4 HNO3 → H2SnO3 + 4 NO2 + H2O
l
bond, therefore soluble in water and form NH4OH or
NH3 (aq ).
l Oxidation of compounds
l Due to basic nature, NH3 is a good complexing agent and 6 FeSO 4 + 3 H2SO 4 + 2 HNO3 →
reducing agent. e.g. 3Fe2 (SO 4 )3 + 2 NO + 4 H2O
2FeCl3 (aq ) + 3NH4OH (aq ) → NO is absorbed by FeSO 4 and a dark brown ring of nitroso
ferrous sulphate is formed (ring test for nitrates).
Fe2O3 ⋅ xH2O(s) + 3 NH4Cl
Brown ppt.
l Metals like iron, cobalt, nickel, chromium, aluminium
ZnSO 4 (aq ) + 2 NH4OH (aq ) → become passive in conc. HNO3 due to the formation of a
Zn(OH)2 (s) + (NH4 )2 SO 4 thin protective film of oxide on the surface of the metal.
White ppt.
