The s-Block Elements Class 11 Notes Chemistry

 Page 1


? s-block elements consists of group-I (Alkali metals) and group-2 (Alkaline
earth metals).
? Group 1
st
 elements—Li, Na, K, Rb, Cs, Fr.
? Group 2
nd
 elements—Be, Mg, Ca, Sr, Ba, Ra.
? Atomic radius—Atomic radius of alkali metals are greater than alkaline
earth metals.
? Hydration enthalpy : Decreases with increases in ionic sizes.
? Ionic mobility : Smaller the size of ion, more highly it is hydrated and
hence lower is its ionic mobility.
Li
+
 < Na
+
 < K
+
 < Rb
+
 < Cs
+
? Ionisation enthalpies : 1
st
 I.E. of group 1
st
 is smaller than group 2
nd
elements but 2
nd
 I.E. of group 2
nd
 is smaller than group 1
st
 elements.
? Flame colouration : Due to low I.E., s-block elements and their salts
imparts characteristics colour of oxidising flame (except Be and Mg). Be
and Mg do not show flame colouration because they have small size and
very high ionisation enthalpy.
? Reducing character : Due to large negative electrode potentials alkali
metals are stronger reducing agent than alkaline earth metal.
? Reactivity towards air :
4Li + O
2
 —? 2Li
2
O (Lithium oxide)
2Na + O
2
 —? Na
2
O
2
 (Sodium peroxide)
M + O
2
 —? MO
2
 (M = K, Rb, Cs metal superoxide)
Alkaline earth metals being smaller in size do not from superoxides.
? Reactivity towards H
2
O :
2M + 2H
2
O —? 2MOH + H
2
Page 2


? s-block elements consists of group-I (Alkali metals) and group-2 (Alkaline
earth metals).
? Group 1
st
 elements—Li, Na, K, Rb, Cs, Fr.
? Group 2
nd
 elements—Be, Mg, Ca, Sr, Ba, Ra.
? Atomic radius—Atomic radius of alkali metals are greater than alkaline
earth metals.
? Hydration enthalpy : Decreases with increases in ionic sizes.
? Ionic mobility : Smaller the size of ion, more highly it is hydrated and
hence lower is its ionic mobility.
Li
+
 < Na
+
 < K
+
 < Rb
+
 < Cs
+
? Ionisation enthalpies : 1
st
 I.E. of group 1
st
 is smaller than group 2
nd
elements but 2
nd
 I.E. of group 2
nd
 is smaller than group 1
st
 elements.
? Flame colouration : Due to low I.E., s-block elements and their salts
imparts characteristics colour of oxidising flame (except Be and Mg). Be
and Mg do not show flame colouration because they have small size and
very high ionisation enthalpy.
? Reducing character : Due to large negative electrode potentials alkali
metals are stronger reducing agent than alkaline earth metal.
? Reactivity towards air :
4Li + O
2
 —? 2Li
2
O (Lithium oxide)
2Na + O
2
 —? Na
2
O
2
 (Sodium peroxide)
M + O
2
 —? MO
2
 (M = K, Rb, Cs metal superoxide)
Alkaline earth metals being smaller in size do not from superoxides.
? Reactivity towards H
2
O :
2M + 2H
2
O —? 2MOH + H
2
  (Alkali metal)
M + 2H
2
O —? M(OH)
2
 + H
2
(Alkaline earth metals)
? Reactivity towards hydrogen :
2M + H
2
 —? 2MH
(M = Li, Na, K, Rb, Cs)
M + H
2
 —? MH
2
(M = Mg, Ca, Sr, Ba)
2BeCl
2
 + LiAlH
4
 —? 2BeH
2
 + LiCl + AlCl
3
.
? Reactivity towards halogens :
2M + X
2
 —? 2MX (M = Li, Na, K, Rb, Cs)
M + X
2
 —? MX
2
 (M = Mg, Ca, Sr, Ba)
BeO + C + Cl
2
 BeCl
2
 + CO
? Solution in liquid ammonia : The fresh solution of alkali metals and
alkaline earth metals (except Be and Mg) is deep blue, paramagnetic and
highly reducing due to presence of ammoniated electrons.
? Solubility of alkaline earth metal carbonate in water :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < RbCO
3
 < Cs
2
CO
3
? Solubility of alkaline earth metal carbonates in water.
BaCO
3
 < SrCO
3
 < CaCO
3
 < MgCO
3
 < BeCO
3
? Solubility of alkaline earth metal sulphates in water :
BaSO
4
 < SrSO
4
 < CaSO
4
 < MgSO
4
 < BeSO
4
? Thermal stability of alkali metal carbonates :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < Rb
2
CO
3
 < Cs
2
CO
3
? Thermal stability of alkaline earth metal carbonates :
BeCO
3
 < MgCO
3
 < CaCO
3
 < SrCO
3
 < BaCO
3
? Anamolous behaviour of Li and Be : It is due to very small size, high
I.E. and high polarising power (i.e., charge/radius)
? Diagonal relationship (similarities) between Li and Mg :
(i) Both Li and Mg are hard.
(ii) Both react with N
2
 to form nitrides.
Page 3


? s-block elements consists of group-I (Alkali metals) and group-2 (Alkaline
earth metals).
? Group 1
st
 elements—Li, Na, K, Rb, Cs, Fr.
? Group 2
nd
 elements—Be, Mg, Ca, Sr, Ba, Ra.
? Atomic radius—Atomic radius of alkali metals are greater than alkaline
earth metals.
? Hydration enthalpy : Decreases with increases in ionic sizes.
? Ionic mobility : Smaller the size of ion, more highly it is hydrated and
hence lower is its ionic mobility.
Li
+
 < Na
+
 < K
+
 < Rb
+
 < Cs
+
? Ionisation enthalpies : 1
st
 I.E. of group 1
st
 is smaller than group 2
nd
elements but 2
nd
 I.E. of group 2
nd
 is smaller than group 1
st
 elements.
? Flame colouration : Due to low I.E., s-block elements and their salts
imparts characteristics colour of oxidising flame (except Be and Mg). Be
and Mg do not show flame colouration because they have small size and
very high ionisation enthalpy.
? Reducing character : Due to large negative electrode potentials alkali
metals are stronger reducing agent than alkaline earth metal.
? Reactivity towards air :
4Li + O
2
 —? 2Li
2
O (Lithium oxide)
2Na + O
2
 —? Na
2
O
2
 (Sodium peroxide)
M + O
2
 —? MO
2
 (M = K, Rb, Cs metal superoxide)
Alkaline earth metals being smaller in size do not from superoxides.
? Reactivity towards H
2
O :
2M + 2H
2
O —? 2MOH + H
2
  (Alkali metal)
M + 2H
2
O —? M(OH)
2
 + H
2
(Alkaline earth metals)
? Reactivity towards hydrogen :
2M + H
2
 —? 2MH
(M = Li, Na, K, Rb, Cs)
M + H
2
 —? MH
2
(M = Mg, Ca, Sr, Ba)
2BeCl
2
 + LiAlH
4
 —? 2BeH
2
 + LiCl + AlCl
3
.
? Reactivity towards halogens :
2M + X
2
 —? 2MX (M = Li, Na, K, Rb, Cs)
M + X
2
 —? MX
2
 (M = Mg, Ca, Sr, Ba)
BeO + C + Cl
2
 BeCl
2
 + CO
? Solution in liquid ammonia : The fresh solution of alkali metals and
alkaline earth metals (except Be and Mg) is deep blue, paramagnetic and
highly reducing due to presence of ammoniated electrons.
? Solubility of alkaline earth metal carbonate in water :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < RbCO
3
 < Cs
2
CO
3
? Solubility of alkaline earth metal carbonates in water.
BaCO
3
 < SrCO
3
 < CaCO
3
 < MgCO
3
 < BeCO
3
? Solubility of alkaline earth metal sulphates in water :
BaSO
4
 < SrSO
4
 < CaSO
4
 < MgSO
4
 < BeSO
4
? Thermal stability of alkali metal carbonates :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < Rb
2
CO
3
 < Cs
2
CO
3
? Thermal stability of alkaline earth metal carbonates :
BeCO
3
 < MgCO
3
 < CaCO
3
 < SrCO
3
 < BaCO
3
? Anamolous behaviour of Li and Be : It is due to very small size, high
I.E. and high polarising power (i.e., charge/radius)
? Diagonal relationship (similarities) between Li and Mg :
(i) Both Li and Mg are hard.
(ii) Both react with N
2
 to form nitrides.
6Li + N
2 
—? 2Li
3
N
 3Mg + N
2 
—? Mg
3
N
2
  (iii)  Decomposition of carbonates :
Li
2
CO
3 
 Li
2
O + CO
2
 MgCO
3
 MgO + CO
2
(iv) Both LiCl and MgCl
2
 are deliquescent. They form hydrates salts 
LiCl.2H
2
O and MgCl
2
.6H
2
O.
(v)  Decomposition of nitrates :
4LiNO
3 
 2Li
2
O + 4NO
2
 + O
2
2Mg(NO
3
)
2
 2MgO + 4NO
2
 + O
2
? Diagonal relationship (similarities) between Be and Al :
(i) Both are passive to acids due to formation of oxide layer.
(ii) Hydroxides of both dissolve in alkali to form [Be(OH)
4
]
2–
 and
[Al(OH)
4
]
–
.
(iii) Chloride of both has bridged structure.
(iv) Both have tendency to form complexes of BeF
4
2–
, AlF
6
3–
.
? Manufacturing of washing soda (Na
2
CO
3
.10H
2
O) :
Solvay process :
NH
3
(g) + CO
2
(g) + H
2
O (l) —? NH
4
HCO
3
 (aq)
NH
4
HCO
3
 (aq) + NaCl (aq) —? NaHCO
3
(s) + NH
4
Cl (aq)
2NaHCO
3
  Na
2
CO
3
 + H
2
O(l) + CO
2
(g)
2NH
4
Cl (aq) + Ca(OH)
2
 ? CaCl
2
(s) + 2H
2
O(l) + 2NH
3
 (g)
? Manufacturing of caustic soda (NaOH) : Castner-Kellner cell.
Cathode : Na
+
 + e
–
 Na-Hg
Anode : Cl
– 
—? + e
–
2Na-Hg + 2H
2
O —? 2NaOH + 2Hg + H
2
? Plaster of paris : (CaSO
4
.½H
2
O)
2(CaSO
4
.2H
2
O) 2(CaSO
4
).H
2
O + 3H
2
O
Gypsum
Page 4


? s-block elements consists of group-I (Alkali metals) and group-2 (Alkaline
earth metals).
? Group 1
st
 elements—Li, Na, K, Rb, Cs, Fr.
? Group 2
nd
 elements—Be, Mg, Ca, Sr, Ba, Ra.
? Atomic radius—Atomic radius of alkali metals are greater than alkaline
earth metals.
? Hydration enthalpy : Decreases with increases in ionic sizes.
? Ionic mobility : Smaller the size of ion, more highly it is hydrated and
hence lower is its ionic mobility.
Li
+
 < Na
+
 < K
+
 < Rb
+
 < Cs
+
? Ionisation enthalpies : 1
st
 I.E. of group 1
st
 is smaller than group 2
nd
elements but 2
nd
 I.E. of group 2
nd
 is smaller than group 1
st
 elements.
? Flame colouration : Due to low I.E., s-block elements and their salts
imparts characteristics colour of oxidising flame (except Be and Mg). Be
and Mg do not show flame colouration because they have small size and
very high ionisation enthalpy.
? Reducing character : Due to large negative electrode potentials alkali
metals are stronger reducing agent than alkaline earth metal.
? Reactivity towards air :
4Li + O
2
 —? 2Li
2
O (Lithium oxide)
2Na + O
2
 —? Na
2
O
2
 (Sodium peroxide)
M + O
2
 —? MO
2
 (M = K, Rb, Cs metal superoxide)
Alkaline earth metals being smaller in size do not from superoxides.
? Reactivity towards H
2
O :
2M + 2H
2
O —? 2MOH + H
2
  (Alkali metal)
M + 2H
2
O —? M(OH)
2
 + H
2
(Alkaline earth metals)
? Reactivity towards hydrogen :
2M + H
2
 —? 2MH
(M = Li, Na, K, Rb, Cs)
M + H
2
 —? MH
2
(M = Mg, Ca, Sr, Ba)
2BeCl
2
 + LiAlH
4
 —? 2BeH
2
 + LiCl + AlCl
3
.
? Reactivity towards halogens :
2M + X
2
 —? 2MX (M = Li, Na, K, Rb, Cs)
M + X
2
 —? MX
2
 (M = Mg, Ca, Sr, Ba)
BeO + C + Cl
2
 BeCl
2
 + CO
? Solution in liquid ammonia : The fresh solution of alkali metals and
alkaline earth metals (except Be and Mg) is deep blue, paramagnetic and
highly reducing due to presence of ammoniated electrons.
? Solubility of alkaline earth metal carbonate in water :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < RbCO
3
 < Cs
2
CO
3
? Solubility of alkaline earth metal carbonates in water.
BaCO
3
 < SrCO
3
 < CaCO
3
 < MgCO
3
 < BeCO
3
? Solubility of alkaline earth metal sulphates in water :
BaSO
4
 < SrSO
4
 < CaSO
4
 < MgSO
4
 < BeSO
4
? Thermal stability of alkali metal carbonates :
Li
2
CO
3
 < Na
2
CO
3
 < K
2
CO
3
 < Rb
2
CO
3
 < Cs
2
CO
3
? Thermal stability of alkaline earth metal carbonates :
BeCO
3
 < MgCO
3
 < CaCO
3
 < SrCO
3
 < BaCO
3
? Anamolous behaviour of Li and Be : It is due to very small size, high
I.E. and high polarising power (i.e., charge/radius)
? Diagonal relationship (similarities) between Li and Mg :
(i) Both Li and Mg are hard.
(ii) Both react with N
2
 to form nitrides.
6Li + N
2 
—? 2Li
3
N
 3Mg + N
2 
—? Mg
3
N
2
  (iii)  Decomposition of carbonates :
Li
2
CO
3 
 Li
2
O + CO
2
 MgCO
3
 MgO + CO
2
(iv) Both LiCl and MgCl
2
 are deliquescent. They form hydrates salts 
LiCl.2H
2
O and MgCl
2
.6H
2
O.
(v)  Decomposition of nitrates :
4LiNO
3 
 2Li
2
O + 4NO
2
 + O
2
2Mg(NO
3
)
2
 2MgO + 4NO
2
 + O
2
? Diagonal relationship (similarities) between Be and Al :
(i) Both are passive to acids due to formation of oxide layer.
(ii) Hydroxides of both dissolve in alkali to form [Be(OH)
4
]
2–
 and
[Al(OH)
4
]
–
.
(iii) Chloride of both has bridged structure.
(iv) Both have tendency to form complexes of BeF
4
2–
, AlF
6
3–
.
? Manufacturing of washing soda (Na
2
CO
3
.10H
2
O) :
Solvay process :
NH
3
(g) + CO
2
(g) + H
2
O (l) —? NH
4
HCO
3
 (aq)
NH
4
HCO
3
 (aq) + NaCl (aq) —? NaHCO
3
(s) + NH
4
Cl (aq)
2NaHCO
3
  Na
2
CO
3
 + H
2
O(l) + CO
2
(g)
2NH
4
Cl (aq) + Ca(OH)
2
 ? CaCl
2
(s) + 2H
2
O(l) + 2NH
3
 (g)
? Manufacturing of caustic soda (NaOH) : Castner-Kellner cell.
Cathode : Na
+
 + e
–
 Na-Hg
Anode : Cl
– 
—? + e
–
2Na-Hg + 2H
2
O —? 2NaOH + 2Hg + H
2
? Plaster of paris : (CaSO
4
.½H
2
O)
2(CaSO
4
.2H
2
O) 2(CaSO
4
).H
2
O + 3H
2
O
Gypsum
? Cement is a finely powdered mixture of calcium silicates and aluminate
along with small quantities of gypsum which sets into a hard stone like
mass when treated with water.