CHAPTER
11 The p-Block Elements
(Group 15 to 18)
Topicwise Trend Analysis of Past 10 Years'
Questions TOPICS
12%
38% 14%
"40% 1. Group 15 Elements
2. Group 16 Elements
27%
27% - 1 3. Group 17 Elements
4. Group 18 Elements
2
2
23%
NEET Analysis JEE Analysis
19%
Facts at Your Tips
Some Trends in p-Block Elements The stability of pentoxides decreases in the order:
" In case of phosphorus trihalides, the Lewis acid strength
decreases in the order :
P,0,< As,0,> Sb,0, > N,O,> Bi,0,
" The acidic strength of oxides of nitrogen increases in the
PF; >PCI, > PBr, > PI, order: N,0 <NO<N,O, <N,O4, <N,0,
and the bond angle increases as the electronegativity of the
Theacidic strength of pentoxides decreases in the order :
halogen decreases down the group i.e.,
N,O,> P,O, >As,0,> Sb,0,> Bi,05
PF, <PCI, <PBr, <PI, " The acidic nature of dioxides and trioxides decreases
Trihalides of P, As and Sb also behave as Lewis acids and the in the
order :
acid strength shows decreasing trend down the group i.e., SO, >SeO, >TeO, > PoO, and S0, >SeO, >TeO,
PCI, >AsCI, > SbCl, In case of hydrides of group 15 elements, melting points and
" The ease of hydrolysis of trihalides of group 15 elements boiling points decrease in the order:
decrease in the order : H,0> H,Te >H,Se >H,S
NCI, >PCI, >AsCl, >SbCl,> BiCl, Volatility increases in the order :
NF, and PF, are not hydrolysed. H,0<H,Te < H,Se <H,S
" For trihalides of N, the stability decreases in the order: Acidic, covalent and reducing characters increase in the
order :
NE, >NCI, > NBr,
and Lewis base strength increases in the order H,0< H,S<H,Se <HTe
NE<NCI, <NBr, <NI, Bond angle, dipole moment and thermal stability decrease
in the order:
The m.pt. of hydrides increases in the order:
PH, <AsH, <SbH, <NH, H,0> H,S> H,Se >H,Te
Acidity and thermal stability of oxoacids having diferent
and the increasing order of b,pt. is PH, <AsH, <NH,< SbH, halogens with the same oxidation number decrease with
e reducing power, poisonous nature and covalent nature increase in atomic number of the halogen. For example,
of hydrides increase in the order : HCIO> HBrO > HIO.
NH, <PH, <AsH, <SbH, <BiH, The acidic character and thermal stability increase in the
" The basic nature, bond angle, thermal stability and dipole order as there is an increase in the oxidation number of the
moment offhydrides (MH) decrease in the order: halogen :
NH, >PH, >AsH, >SbH, >BiH, HCIO <HCIO, <HCIO, <HCIO04
The p-8lock Elements (Group 15 to 18) 379
, decreases in the order: whereas the acidicstrength and reducing character
The oxidising power in the order :
HCIO> HCIO, > HCIO, > HClo, HF < HCI <HBr< HI increase
of these acids follows the
The strength of the conjugate bases In case of diatomic molecules (X,) of
order :
CIO >Clo, >Cl0; >Cloj.
dissociation energy decreases in the order. halogens, the
order : Cl, > Br, >> F, > 1,
The stability of anions of oxoacids increases in the the oxidising power, solubility in water and
CIO <CIO, <ClO, <ClO,. decrease in the order:
reactivit;
Oxides of chlorine, bromine and iodine are acidic and the F, > Cl, > Br, > I,
acidic character increases as the percentage of oxygen in
For a particular non-metal atom(M), the
them increases.
bond (covalent) decreases in the order: strength of M-
In case of oxidesof chlorine the decreasing order of oxidising M-F> M Cl > M Br > M-I
power is :
For the same metal atomn (M), the ionic character of M .
Ci,0,> Cl,0,> ClO, > Cl,0 bond, melting point and boiling point of halides
The increasing order of stability is the order : decrease in
Cl,0< ClO,<Cl,O,< Cl,O, M-F> M-Cl> M- Br > M-I
HIis least stable of all hydrogen halides and decomposes In case of halide ions (X), the heat of hydration and baci.
to H, and I,. This is the reason that a bottle containing HI character decrease in the order:
acquires brown colour due to liberation ofI, after some time. F>C> Br > I
In case of (hydrogen halides, HX) of group 17 elements, the and reducing character increases in the order :
boiling points increases in the order: F<CI< Br <I
HCl < HBr <HI< HF In case of group 17 elements (X), the electronegativity,
and the volatility decreases in the order : reactivity and non-metallic character decrease in the order:
HCl> HBr > HI> HF F> Cl> Br >I.
The thermal stability, dipole moment and bond strength The negative electron gain enthalpy decrease in the order:
decrease in the order : Cl> F> Br>I
HF> HCI >HBr> HI and the basic character increase in the order : F<Cl< Br<l
Group 15 Elements (Nitrogen Family) Arsenic (As) 33 [Ar] 3d°4s 4p -3, +3, +5
Group 15 of the periodic table consists of six elements viz.
Antimony (Sb) 51 (Kr]4d'sssp' -3,+3, +5
nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb)
bismuth (Bi) and moscovium (Mc). Bismuth (Bi) 83 [Xe] 4f45a6s6p+3, +5
Occurrence : Molecular nitrogen comprises 78% by volume Moscovium
of the atmosphere. In earth's crust, it occurs as sodium nitrate (Mc) 115 (Rn] 5fl6a°7s7p
and potassium nitrate. In plants and animals it is found in General Characteristics
the form of proteins. Phosphorus is the main component of
phosphate rocks and essential constituent of animal and plant Physical state N, (unreactive gas), P, (solid non
and metallic metal), As, and Sb, (Solid metalloids),
matter. As, Sb and Bi are found mainly as sulphide minerals.
character Bi (metal)
Electronic Configuration: The electronic configuration of Atomic radii Increase down the group, smaller
these elements is ns' np. than that of group 14 elementsdue to
The three p-electrons are equally distributed in accordance increased nuclear charge.
with Hund's rule amongst the three orbitals p, P, and p. |Melting and M.pt. increases from N to As and then
and since the orbitals are exactly half filled, the elements are boiling points decreases whereas b.pt. increases trom
fairly stable and not so reactive. N to Sb and decreases very slightiy.
Lonisation Decreases regularly down the group ue
Element At. Electronic Oxidation
No.
enthalpy to increase in size.
Configuration State
-1, -2, -3, 0,
Electronegativity Decreases down the group.
Nitrogen (N) 7 [He] 2s2p +1, +2, +3, Allotropy Nitrogen (a and B-Nitrogen), phosphors
+4, +5 (white, red, scarlet, violet, a-black,
B-black), arsenic (grey, yellow, black)»
Phosphorus (P) 15(Ne] 3s'3p -3, +3, +5
antimony (metallic, yellow, explosive).
380 Chemistry
, They exhibit the property of
Catenation
catenation
but to lesser extent due to weak " The acidic nature of pentoxides decreases from N,O, to
bond than group 14 elements.
M- M Bi,0s
Elemental nitrogen is highly unreactive Acidic nature of M,0, oxides also decreases from N,O, to
Reactivity
Bi,O4. The acidic nature of these oxides is less than M,Os
because of its strong triple bond. type and more than M,0, type. The decrease in acidic nature
(almost as inert as noble gases). White of the oxides from nitrogen to bismuth is due to decrease in
phosphorus is extremely reactive non-metallic character and increase in metallic character
kept in water. It is inflammable and and
can from N to Bi.
be ignited at 45° C. " Besides these three type of oxides, nitrogen forms two more
Chemical Properties oxides N,O and NO (these are neutral) and bismuth forms
bismuth monoxide (BiO).
Hydrides
Acidic
All the elements of group 15 form MH, type hydrides. N,O, P,0, As,0, Sb,0,Bi,O, nature
Because of the decrease in the strength of M-H bond (due N,0, P,0, As,0, Sb,O, Bi,0, increases
to the increase in atomic size of the element) the thermal N,O, P,0,As,0, Sb,O, Bi,O,
stability of these hydrides decreases gradually from NH,
Acidic nature decreases
to BiH3.
. Because of the decrease in thermal stability, the tendency Halides
of these hydrides to give hydrogen and thus act as reducing Nitrogen forms MX, type of halides while rest other form
agent gradually increases as we move from NH, to BiH,. both MX, and MXs types of halides.
" As the size of the central atom increases, the stability of In solid state, PCl, exists as (PCL]* and [PCI,] having
conjugate acid decreases and hence the basic character tetrahedral and octahedral structures respectively.
decreases in the order : PBr, exists in solid state as [PBr,]* (Br]while PI, exists as
NH, > PH, > AsH, > SbH, > BiH, [PIJ" (I] in solution.
Hydrogen bonding is present in ammonia as nitrogen In case of phosphorus trihalides, PX, (X = F, CI, Br, I), the
is small in size and is highly electronegative. NH, forms bond angles increases from PF, to PI, as the electronegativity
H-bonds but electronegativity of the rest of the elements is of the halogen decreases fromn F to I. A more electronegative
nearly equal to hydrogen, hence other hydrides of this group atom will have higher tendency to keep the bonding pair
do not exhibit H-bonding. more towards itself with the result, the electron cloud is
drawn away from the central atom. This leads to decrease
" All the hydrides of group 15 elements have pyramidal
structures. The bond angle HMH is less than the ideal in bond pair-bond pair repulsions. Consequently, the bond
tetrahedral angle of 109°28. As we go down the group, angle increases as the electronegativity of substituents on P
decreases.
the size of atom increases and electronegativity decreases.
Electron density and hence repulsion of lone pair of Stability :NE, >NCI,> NBr,
electrons decreases. sp hybridisation becomes less and less Lewis acid strength : PCI, > AsCl, > SbC, and
distinct with increasing size of central atom, hence bond PF > PCl, > PBr, > PI,
angle decreases from NH, to BiH,. Lewis basestrength: NI, >NBr, >NCI, > NE,
Melting point : PH, <AsH, < SbH, < NH, Bond angle : PF, < PCl, <PBr, < Pl,
Boiling point: BilH, > SbH,> NH, > AsH, > PH, Anomalous Behaviour of Nitrogen
Bond angle: NH, > PH,> AsH, > SbH, > BiH, " Nitrogen occurs in free state but others do not.
(107.8°) (93.6°) (91.8°) (91.3°) (90.0)
Nitrogen is a gas, while other elements are solids.
Stability, Basic character, Bond angle, Nitrogen molecule is diatomic (N) while molecules of
Strength of MH bond decrease. P,As and Sb are tetra atomic (P, As,, Sb,) and that of Bi is
monoatomic.
NH,, PH, AsH,, SbH, BiH, It is chemically inert due to the presence of triple bond,
Reducing character, Acidic character, other elements are highly reactive due to presence of single
Poisonous character increase. bond in their molecule.
N=N, C=0, (C=N) are isoelectronic species but NEN
Oxides is less reactive due to non-polar nature and high ionisation
M,04and
All these elements form oxides of the types M,O, energy.
M,Os Their acid strength
Nitrogen does not form sulphides.
ne trioxides of N. P and As are acidic. Halides of nitrogen except NF, are highly explosive.
As,O,
decreases in the order::N,0, > P,0, >while that of bismuth N,O, and N,O, are monomeric while trioxides and
Thet trioxide of antimony is amphoteric
pentoxides of P, As and Sb are dimeric.
basic.
381
The p-Block Elements (Group 15 to 18)
11 The p-Block Elements
(Group 15 to 18)
Topicwise Trend Analysis of Past 10 Years'
Questions TOPICS
12%
38% 14%
"40% 1. Group 15 Elements
2. Group 16 Elements
27%
27% - 1 3. Group 17 Elements
4. Group 18 Elements
2
2
23%
NEET Analysis JEE Analysis
19%
Facts at Your Tips
Some Trends in p-Block Elements The stability of pentoxides decreases in the order:
" In case of phosphorus trihalides, the Lewis acid strength
decreases in the order :
P,0,< As,0,> Sb,0, > N,O,> Bi,0,
" The acidic strength of oxides of nitrogen increases in the
PF; >PCI, > PBr, > PI, order: N,0 <NO<N,O, <N,O4, <N,0,
and the bond angle increases as the electronegativity of the
Theacidic strength of pentoxides decreases in the order :
halogen decreases down the group i.e.,
N,O,> P,O, >As,0,> Sb,0,> Bi,05
PF, <PCI, <PBr, <PI, " The acidic nature of dioxides and trioxides decreases
Trihalides of P, As and Sb also behave as Lewis acids and the in the
order :
acid strength shows decreasing trend down the group i.e., SO, >SeO, >TeO, > PoO, and S0, >SeO, >TeO,
PCI, >AsCI, > SbCl, In case of hydrides of group 15 elements, melting points and
" The ease of hydrolysis of trihalides of group 15 elements boiling points decrease in the order:
decrease in the order : H,0> H,Te >H,Se >H,S
NCI, >PCI, >AsCl, >SbCl,> BiCl, Volatility increases in the order :
NF, and PF, are not hydrolysed. H,0<H,Te < H,Se <H,S
" For trihalides of N, the stability decreases in the order: Acidic, covalent and reducing characters increase in the
order :
NE, >NCI, > NBr,
and Lewis base strength increases in the order H,0< H,S<H,Se <HTe
NE<NCI, <NBr, <NI, Bond angle, dipole moment and thermal stability decrease
in the order:
The m.pt. of hydrides increases in the order:
PH, <AsH, <SbH, <NH, H,0> H,S> H,Se >H,Te
Acidity and thermal stability of oxoacids having diferent
and the increasing order of b,pt. is PH, <AsH, <NH,< SbH, halogens with the same oxidation number decrease with
e reducing power, poisonous nature and covalent nature increase in atomic number of the halogen. For example,
of hydrides increase in the order : HCIO> HBrO > HIO.
NH, <PH, <AsH, <SbH, <BiH, The acidic character and thermal stability increase in the
" The basic nature, bond angle, thermal stability and dipole order as there is an increase in the oxidation number of the
moment offhydrides (MH) decrease in the order: halogen :
NH, >PH, >AsH, >SbH, >BiH, HCIO <HCIO, <HCIO, <HCIO04
The p-8lock Elements (Group 15 to 18) 379
, decreases in the order: whereas the acidicstrength and reducing character
The oxidising power in the order :
HCIO> HCIO, > HCIO, > HClo, HF < HCI <HBr< HI increase
of these acids follows the
The strength of the conjugate bases In case of diatomic molecules (X,) of
order :
CIO >Clo, >Cl0; >Cloj.
dissociation energy decreases in the order. halogens, the
order : Cl, > Br, >> F, > 1,
The stability of anions of oxoacids increases in the the oxidising power, solubility in water and
CIO <CIO, <ClO, <ClO,. decrease in the order:
reactivit;
Oxides of chlorine, bromine and iodine are acidic and the F, > Cl, > Br, > I,
acidic character increases as the percentage of oxygen in
For a particular non-metal atom(M), the
them increases.
bond (covalent) decreases in the order: strength of M-
In case of oxidesof chlorine the decreasing order of oxidising M-F> M Cl > M Br > M-I
power is :
For the same metal atomn (M), the ionic character of M .
Ci,0,> Cl,0,> ClO, > Cl,0 bond, melting point and boiling point of halides
The increasing order of stability is the order : decrease in
Cl,0< ClO,<Cl,O,< Cl,O, M-F> M-Cl> M- Br > M-I
HIis least stable of all hydrogen halides and decomposes In case of halide ions (X), the heat of hydration and baci.
to H, and I,. This is the reason that a bottle containing HI character decrease in the order:
acquires brown colour due to liberation ofI, after some time. F>C> Br > I
In case of (hydrogen halides, HX) of group 17 elements, the and reducing character increases in the order :
boiling points increases in the order: F<CI< Br <I
HCl < HBr <HI< HF In case of group 17 elements (X), the electronegativity,
and the volatility decreases in the order : reactivity and non-metallic character decrease in the order:
HCl> HBr > HI> HF F> Cl> Br >I.
The thermal stability, dipole moment and bond strength The negative electron gain enthalpy decrease in the order:
decrease in the order : Cl> F> Br>I
HF> HCI >HBr> HI and the basic character increase in the order : F<Cl< Br<l
Group 15 Elements (Nitrogen Family) Arsenic (As) 33 [Ar] 3d°4s 4p -3, +3, +5
Group 15 of the periodic table consists of six elements viz.
Antimony (Sb) 51 (Kr]4d'sssp' -3,+3, +5
nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb)
bismuth (Bi) and moscovium (Mc). Bismuth (Bi) 83 [Xe] 4f45a6s6p+3, +5
Occurrence : Molecular nitrogen comprises 78% by volume Moscovium
of the atmosphere. In earth's crust, it occurs as sodium nitrate (Mc) 115 (Rn] 5fl6a°7s7p
and potassium nitrate. In plants and animals it is found in General Characteristics
the form of proteins. Phosphorus is the main component of
phosphate rocks and essential constituent of animal and plant Physical state N, (unreactive gas), P, (solid non
and metallic metal), As, and Sb, (Solid metalloids),
matter. As, Sb and Bi are found mainly as sulphide minerals.
character Bi (metal)
Electronic Configuration: The electronic configuration of Atomic radii Increase down the group, smaller
these elements is ns' np. than that of group 14 elementsdue to
The three p-electrons are equally distributed in accordance increased nuclear charge.
with Hund's rule amongst the three orbitals p, P, and p. |Melting and M.pt. increases from N to As and then
and since the orbitals are exactly half filled, the elements are boiling points decreases whereas b.pt. increases trom
fairly stable and not so reactive. N to Sb and decreases very slightiy.
Lonisation Decreases regularly down the group ue
Element At. Electronic Oxidation
No.
enthalpy to increase in size.
Configuration State
-1, -2, -3, 0,
Electronegativity Decreases down the group.
Nitrogen (N) 7 [He] 2s2p +1, +2, +3, Allotropy Nitrogen (a and B-Nitrogen), phosphors
+4, +5 (white, red, scarlet, violet, a-black,
B-black), arsenic (grey, yellow, black)»
Phosphorus (P) 15(Ne] 3s'3p -3, +3, +5
antimony (metallic, yellow, explosive).
380 Chemistry
, They exhibit the property of
Catenation
catenation
but to lesser extent due to weak " The acidic nature of pentoxides decreases from N,O, to
bond than group 14 elements.
M- M Bi,0s
Elemental nitrogen is highly unreactive Acidic nature of M,0, oxides also decreases from N,O, to
Reactivity
Bi,O4. The acidic nature of these oxides is less than M,Os
because of its strong triple bond. type and more than M,0, type. The decrease in acidic nature
(almost as inert as noble gases). White of the oxides from nitrogen to bismuth is due to decrease in
phosphorus is extremely reactive non-metallic character and increase in metallic character
kept in water. It is inflammable and and
can from N to Bi.
be ignited at 45° C. " Besides these three type of oxides, nitrogen forms two more
Chemical Properties oxides N,O and NO (these are neutral) and bismuth forms
bismuth monoxide (BiO).
Hydrides
Acidic
All the elements of group 15 form MH, type hydrides. N,O, P,0, As,0, Sb,0,Bi,O, nature
Because of the decrease in the strength of M-H bond (due N,0, P,0, As,0, Sb,O, Bi,0, increases
to the increase in atomic size of the element) the thermal N,O, P,0,As,0, Sb,O, Bi,O,
stability of these hydrides decreases gradually from NH,
Acidic nature decreases
to BiH3.
. Because of the decrease in thermal stability, the tendency Halides
of these hydrides to give hydrogen and thus act as reducing Nitrogen forms MX, type of halides while rest other form
agent gradually increases as we move from NH, to BiH,. both MX, and MXs types of halides.
" As the size of the central atom increases, the stability of In solid state, PCl, exists as (PCL]* and [PCI,] having
conjugate acid decreases and hence the basic character tetrahedral and octahedral structures respectively.
decreases in the order : PBr, exists in solid state as [PBr,]* (Br]while PI, exists as
NH, > PH, > AsH, > SbH, > BiH, [PIJ" (I] in solution.
Hydrogen bonding is present in ammonia as nitrogen In case of phosphorus trihalides, PX, (X = F, CI, Br, I), the
is small in size and is highly electronegative. NH, forms bond angles increases from PF, to PI, as the electronegativity
H-bonds but electronegativity of the rest of the elements is of the halogen decreases fromn F to I. A more electronegative
nearly equal to hydrogen, hence other hydrides of this group atom will have higher tendency to keep the bonding pair
do not exhibit H-bonding. more towards itself with the result, the electron cloud is
drawn away from the central atom. This leads to decrease
" All the hydrides of group 15 elements have pyramidal
structures. The bond angle HMH is less than the ideal in bond pair-bond pair repulsions. Consequently, the bond
tetrahedral angle of 109°28. As we go down the group, angle increases as the electronegativity of substituents on P
decreases.
the size of atom increases and electronegativity decreases.
Electron density and hence repulsion of lone pair of Stability :NE, >NCI,> NBr,
electrons decreases. sp hybridisation becomes less and less Lewis acid strength : PCI, > AsCl, > SbC, and
distinct with increasing size of central atom, hence bond PF > PCl, > PBr, > PI,
angle decreases from NH, to BiH,. Lewis basestrength: NI, >NBr, >NCI, > NE,
Melting point : PH, <AsH, < SbH, < NH, Bond angle : PF, < PCl, <PBr, < Pl,
Boiling point: BilH, > SbH,> NH, > AsH, > PH, Anomalous Behaviour of Nitrogen
Bond angle: NH, > PH,> AsH, > SbH, > BiH, " Nitrogen occurs in free state but others do not.
(107.8°) (93.6°) (91.8°) (91.3°) (90.0)
Nitrogen is a gas, while other elements are solids.
Stability, Basic character, Bond angle, Nitrogen molecule is diatomic (N) while molecules of
Strength of MH bond decrease. P,As and Sb are tetra atomic (P, As,, Sb,) and that of Bi is
monoatomic.
NH,, PH, AsH,, SbH, BiH, It is chemically inert due to the presence of triple bond,
Reducing character, Acidic character, other elements are highly reactive due to presence of single
Poisonous character increase. bond in their molecule.
N=N, C=0, (C=N) are isoelectronic species but NEN
Oxides is less reactive due to non-polar nature and high ionisation
M,04and
All these elements form oxides of the types M,O, energy.
M,Os Their acid strength
Nitrogen does not form sulphides.
ne trioxides of N. P and As are acidic. Halides of nitrogen except NF, are highly explosive.
As,O,
decreases in the order::N,0, > P,0, >while that of bismuth N,O, and N,O, are monomeric while trioxides and
Thet trioxide of antimony is amphoteric
pentoxides of P, As and Sb are dimeric.
basic.
381
The p-Block Elements (Group 15 to 18)
