Notes : Sequences & Series Class 11 Notes | EduRev

Class 11 : Notes : Sequences & Series Class 11 Notes | EduRev

 Page 1


109 
 
CHAPTER 9 
HYDROGEN 
? Position of Hydrogen in Periodic Table 
? Lightest element known having atomic number 1.  
? Dihydrogen 
? It resembles both alkali metals and halogens and therefore, its position is 
anomalous.  
? In modern periodic table it is located separately 
?Resemblance with alkali metals:- 
1.  Electronic configuration 
1
H = 1s
1
    11
Na = 1s
2
, 2s
2
, 2p
6
, 3s
1
    19
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
6
, 4s
1 
2. Electropositive character:  H
+
, Na
+
, K
+
 etc. 
3. Oxidation state:  +1 
4. Combination with electronegative elements: form binary compounds with 
electronegative elements like alkali metals. 
          Halides:  HClNaCl, KCletc 
Sulphides: H
2
S         Na
2
S, K
2
S     etc 
?Resemblance with halogens:- 
1. Electronic configuration: 
Both contain one electron less than the nearest noble gas configuration 
1
H = 1s
1
 (near to 
2
He) 
9
F = 1s
2
, 2s
2
, 2p
5 
(near to 
8
Ne) 
                         17
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
5 
(near to 
18
Ar) 
2. Non-metallic character: like halogens, hydrogen is non-metallic in nature.  
3. Atomicity: Diatomic molecules. 
4. Formation of similar types of compounds: 
i. Halides: CCl
4
, SiCl
4
, GeCl
4
 
ii. Hydrides: CH
4
, SiH
4
, GeH
4
 
5. Oxidation state:   –1 
      Na
+1
H
-1
                 Na
+1
Cl
-1
 
?Difference from alkali metals:- 
1) Ionization enthalpy: - the ionization enthalpy of hydrogen is very high in 
comparison to alkali metals. 
2) Non- metallic character: alkali metals are typical metals while hydrogen is 
non-metal 
3) Atomicity: hydrogen is diatomic while alkali metals are monoatomic. 
4) Nature of compounds: the compounds of hydrogen are predominantly 
covalent while those of alkali metals are ionic. For example: HCl is covalent 
while NaCl is ionic. 
The oxides of alkali metals are basic while hydrogen oxide is neutral.  
Page 2


109 
 
CHAPTER 9 
HYDROGEN 
? Position of Hydrogen in Periodic Table 
? Lightest element known having atomic number 1.  
? Dihydrogen 
? It resembles both alkali metals and halogens and therefore, its position is 
anomalous.  
? In modern periodic table it is located separately 
?Resemblance with alkali metals:- 
1.  Electronic configuration 
1
H = 1s
1
    11
Na = 1s
2
, 2s
2
, 2p
6
, 3s
1
    19
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
6
, 4s
1 
2. Electropositive character:  H
+
, Na
+
, K
+
 etc. 
3. Oxidation state:  +1 
4. Combination with electronegative elements: form binary compounds with 
electronegative elements like alkali metals. 
          Halides:  HClNaCl, KCletc 
Sulphides: H
2
S         Na
2
S, K
2
S     etc 
?Resemblance with halogens:- 
1. Electronic configuration: 
Both contain one electron less than the nearest noble gas configuration 
1
H = 1s
1
 (near to 
2
He) 
9
F = 1s
2
, 2s
2
, 2p
5 
(near to 
8
Ne) 
                         17
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
5 
(near to 
18
Ar) 
2. Non-metallic character: like halogens, hydrogen is non-metallic in nature.  
3. Atomicity: Diatomic molecules. 
4. Formation of similar types of compounds: 
i. Halides: CCl
4
, SiCl
4
, GeCl
4
 
ii. Hydrides: CH
4
, SiH
4
, GeH
4
 
5. Oxidation state:   –1 
      Na
+1
H
-1
                 Na
+1
Cl
-1
 
?Difference from alkali metals:- 
1) Ionization enthalpy: - the ionization enthalpy of hydrogen is very high in 
comparison to alkali metals. 
2) Non- metallic character: alkali metals are typical metals while hydrogen is 
non-metal 
3) Atomicity: hydrogen is diatomic while alkali metals are monoatomic. 
4) Nature of compounds: the compounds of hydrogen are predominantly 
covalent while those of alkali metals are ionic. For example: HCl is covalent 
while NaCl is ionic. 
The oxides of alkali metals are basic while hydrogen oxide is neutral.  
110 
 
?Difference from halogens:- 
1) Less tendency for hydride formation:Hydrogen has less tendency to take up 
electron to form hydride ion (H
-
) as compared to the halogens which from 
halide ions (X
-
) very easily. 
2) Absence of unshared pairs of electrons : 
3) Nature of oxides: The oxides of halogens are acidic while hydrogen oxide is 
neutral.  
 
? Occurrence of Hydrogen: 
? Hydrogen, the most abundant element in the universe and the third most 
abundant on the surface of the globe, is being visualised as the major future 
source of energy 
?Isotopes of hydrogen:- 
S.N. Property Protium Deuterium Tritium 
1 Relative abudance 99.985 % 0.015 % 10
-15
% 
2 Relative atomic mass 1.007825  2.014102  3.016 
3 Radioactive stability Non-
radioactive 
Non-
radioactive 
Radioactive  
t
1/2
 = 12.334 
yrs 
? Preparation: 
?Methods for commercial production of dihydrogen 
1. Electrolysis of water 
2H
2
O(l)                                           2H
2
(g)  O
2
(g) 
? The hydrogen prepared by this method is of very high purity. However, this 
method is not commonly used because it is very expensive. This method is can 
be used only at those places where the electricity is cheap.  
2. By the reaction of steam on coke :- 
C   +  H
2
O(g)           CO  + H
2
 
Water gas 
? Since the mixture of CO and H
2
 is used for the synthesis of methanol and a 
number of hydrocarbons, it is also called synthesis gas or syn gas. 
? The process of producing syn gas from coal or coke is called coal gasification.  
 
CO  +  H
2
  +  H
2
O                                        CO
2
  +  2H
2
 
Water gas      steam 
? This reaction is called water gas shift reaction. 
 
 
 
 
 
 
Page 3


109 
 
CHAPTER 9 
HYDROGEN 
? Position of Hydrogen in Periodic Table 
? Lightest element known having atomic number 1.  
? Dihydrogen 
? It resembles both alkali metals and halogens and therefore, its position is 
anomalous.  
? In modern periodic table it is located separately 
?Resemblance with alkali metals:- 
1.  Electronic configuration 
1
H = 1s
1
    11
Na = 1s
2
, 2s
2
, 2p
6
, 3s
1
    19
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
6
, 4s
1 
2. Electropositive character:  H
+
, Na
+
, K
+
 etc. 
3. Oxidation state:  +1 
4. Combination with electronegative elements: form binary compounds with 
electronegative elements like alkali metals. 
          Halides:  HClNaCl, KCletc 
Sulphides: H
2
S         Na
2
S, K
2
S     etc 
?Resemblance with halogens:- 
1. Electronic configuration: 
Both contain one electron less than the nearest noble gas configuration 
1
H = 1s
1
 (near to 
2
He) 
9
F = 1s
2
, 2s
2
, 2p
5 
(near to 
8
Ne) 
                         17
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
5 
(near to 
18
Ar) 
2. Non-metallic character: like halogens, hydrogen is non-metallic in nature.  
3. Atomicity: Diatomic molecules. 
4. Formation of similar types of compounds: 
i. Halides: CCl
4
, SiCl
4
, GeCl
4
 
ii. Hydrides: CH
4
, SiH
4
, GeH
4
 
5. Oxidation state:   –1 
      Na
+1
H
-1
                 Na
+1
Cl
-1
 
?Difference from alkali metals:- 
1) Ionization enthalpy: - the ionization enthalpy of hydrogen is very high in 
comparison to alkali metals. 
2) Non- metallic character: alkali metals are typical metals while hydrogen is 
non-metal 
3) Atomicity: hydrogen is diatomic while alkali metals are monoatomic. 
4) Nature of compounds: the compounds of hydrogen are predominantly 
covalent while those of alkali metals are ionic. For example: HCl is covalent 
while NaCl is ionic. 
The oxides of alkali metals are basic while hydrogen oxide is neutral.  
110 
 
?Difference from halogens:- 
1) Less tendency for hydride formation:Hydrogen has less tendency to take up 
electron to form hydride ion (H
-
) as compared to the halogens which from 
halide ions (X
-
) very easily. 
2) Absence of unshared pairs of electrons : 
3) Nature of oxides: The oxides of halogens are acidic while hydrogen oxide is 
neutral.  
 
? Occurrence of Hydrogen: 
? Hydrogen, the most abundant element in the universe and the third most 
abundant on the surface of the globe, is being visualised as the major future 
source of energy 
?Isotopes of hydrogen:- 
S.N. Property Protium Deuterium Tritium 
1 Relative abudance 99.985 % 0.015 % 10
-15
% 
2 Relative atomic mass 1.007825  2.014102  3.016 
3 Radioactive stability Non-
radioactive 
Non-
radioactive 
Radioactive  
t
1/2
 = 12.334 
yrs 
? Preparation: 
?Methods for commercial production of dihydrogen 
1. Electrolysis of water 
2H
2
O(l)                                           2H
2
(g)  O
2
(g) 
? The hydrogen prepared by this method is of very high purity. However, this 
method is not commonly used because it is very expensive. This method is can 
be used only at those places where the electricity is cheap.  
2. By the reaction of steam on coke :- 
C   +  H
2
O(g)           CO  + H
2
 
Water gas 
? Since the mixture of CO and H
2
 is used for the synthesis of methanol and a 
number of hydrocarbons, it is also called synthesis gas or syn gas. 
? The process of producing syn gas from coal or coke is called coal gasification.  
 
CO  +  H
2
  +  H
2
O                                        CO
2
  +  2H
2
 
Water gas      steam 
? This reaction is called water gas shift reaction. 
 
 
 
 
 
 
111 
 
?Properties of Hydrogen:- 
?Physical Properties:- 
1) It is slightly soluble in water (about 2 %) 
2) It is highly combustible and therefore should be handled carefully.  
3) It lightest substance. The weight of one litre hydrogen at NTP is only 0.0899 g. 
?Chemical properties:-Not very reactive due to high bond dissociation energy 
(435.88 kJ mol
-1
 at 298.2 K) 
(i)Combustion: - It burns with pale blue flame  
                    2H
2
 (g) + O
2
 (g)                                2H
2
O(l)
 
(ii) Reaction with metals:-Reactive metals like Na, K, Ca, Li and form hydrides. 
Ca  +  H
2
CaH
2
 
? Metals like Pt, Pd, Ni (elements of d block) form interstitial hydrides by 
absorbing large volume of hydrogen. Such hydrogen is called ‘occluded 
hydrogen and this property of adsorption of a gas by a metal is called occlusion.  
(iii) Reaction with metal oxides:-Hydrogen reduces oxides of less active metals to 
corresponding metal. 
Fe
3
O
4
  +  4H
2
3Fe  +  4H
2
O 
CuO  +  H
2
  Cu  +  H
2
O 
(iv) Reaction with non-metals:- 
3H
2 
(g) + N
2 
(g)                               ?2NH
3
(g)  { Haber process} 
H = - 92.6 kj/mole 
 
2H
2
 (g)+  O
2
 (g)  2H
2
OH = - 285.9 kj/mole 
 
(v) Reaction with carbon monoxide:- 
CO  +  H
2
                                     CH
3
OH 
(vi) Reaction with unsaturated Hydrocarbons:- 
(a) H
2
C = CH
2
  +  H
2
                                       H
3
C – CH
3 
(b) Hydroformylation of olefins to aldehydes:Hydroformilation or Oxo process
 
 RCH = CH
2
  +  H
2
  +  CO                                                    RCH
2
CH
2
CHO 
(c) Hydrogenation of oils:-Vegetable oils are polyun-saturated in nature. The C 
=C bonds in oils can easily undergo oxidation and the oil becomes rancid i.e., 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
Page 4


109 
 
CHAPTER 9 
HYDROGEN 
? Position of Hydrogen in Periodic Table 
? Lightest element known having atomic number 1.  
? Dihydrogen 
? It resembles both alkali metals and halogens and therefore, its position is 
anomalous.  
? In modern periodic table it is located separately 
?Resemblance with alkali metals:- 
1.  Electronic configuration 
1
H = 1s
1
    11
Na = 1s
2
, 2s
2
, 2p
6
, 3s
1
    19
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
6
, 4s
1 
2. Electropositive character:  H
+
, Na
+
, K
+
 etc. 
3. Oxidation state:  +1 
4. Combination with electronegative elements: form binary compounds with 
electronegative elements like alkali metals. 
          Halides:  HClNaCl, KCletc 
Sulphides: H
2
S         Na
2
S, K
2
S     etc 
?Resemblance with halogens:- 
1. Electronic configuration: 
Both contain one electron less than the nearest noble gas configuration 
1
H = 1s
1
 (near to 
2
He) 
9
F = 1s
2
, 2s
2
, 2p
5 
(near to 
8
Ne) 
                         17
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
5 
(near to 
18
Ar) 
2. Non-metallic character: like halogens, hydrogen is non-metallic in nature.  
3. Atomicity: Diatomic molecules. 
4. Formation of similar types of compounds: 
i. Halides: CCl
4
, SiCl
4
, GeCl
4
 
ii. Hydrides: CH
4
, SiH
4
, GeH
4
 
5. Oxidation state:   –1 
      Na
+1
H
-1
                 Na
+1
Cl
-1
 
?Difference from alkali metals:- 
1) Ionization enthalpy: - the ionization enthalpy of hydrogen is very high in 
comparison to alkali metals. 
2) Non- metallic character: alkali metals are typical metals while hydrogen is 
non-metal 
3) Atomicity: hydrogen is diatomic while alkali metals are monoatomic. 
4) Nature of compounds: the compounds of hydrogen are predominantly 
covalent while those of alkali metals are ionic. For example: HCl is covalent 
while NaCl is ionic. 
The oxides of alkali metals are basic while hydrogen oxide is neutral.  
110 
 
?Difference from halogens:- 
1) Less tendency for hydride formation:Hydrogen has less tendency to take up 
electron to form hydride ion (H
-
) as compared to the halogens which from 
halide ions (X
-
) very easily. 
2) Absence of unshared pairs of electrons : 
3) Nature of oxides: The oxides of halogens are acidic while hydrogen oxide is 
neutral.  
 
? Occurrence of Hydrogen: 
? Hydrogen, the most abundant element in the universe and the third most 
abundant on the surface of the globe, is being visualised as the major future 
source of energy 
?Isotopes of hydrogen:- 
S.N. Property Protium Deuterium Tritium 
1 Relative abudance 99.985 % 0.015 % 10
-15
% 
2 Relative atomic mass 1.007825  2.014102  3.016 
3 Radioactive stability Non-
radioactive 
Non-
radioactive 
Radioactive  
t
1/2
 = 12.334 
yrs 
? Preparation: 
?Methods for commercial production of dihydrogen 
1. Electrolysis of water 
2H
2
O(l)                                           2H
2
(g)  O
2
(g) 
? The hydrogen prepared by this method is of very high purity. However, this 
method is not commonly used because it is very expensive. This method is can 
be used only at those places where the electricity is cheap.  
2. By the reaction of steam on coke :- 
C   +  H
2
O(g)           CO  + H
2
 
Water gas 
? Since the mixture of CO and H
2
 is used for the synthesis of methanol and a 
number of hydrocarbons, it is also called synthesis gas or syn gas. 
? The process of producing syn gas from coal or coke is called coal gasification.  
 
CO  +  H
2
  +  H
2
O                                        CO
2
  +  2H
2
 
Water gas      steam 
? This reaction is called water gas shift reaction. 
 
 
 
 
 
 
111 
 
?Properties of Hydrogen:- 
?Physical Properties:- 
1) It is slightly soluble in water (about 2 %) 
2) It is highly combustible and therefore should be handled carefully.  
3) It lightest substance. The weight of one litre hydrogen at NTP is only 0.0899 g. 
?Chemical properties:-Not very reactive due to high bond dissociation energy 
(435.88 kJ mol
-1
 at 298.2 K) 
(i)Combustion: - It burns with pale blue flame  
                    2H
2
 (g) + O
2
 (g)                                2H
2
O(l)
 
(ii) Reaction with metals:-Reactive metals like Na, K, Ca, Li and form hydrides. 
Ca  +  H
2
CaH
2
 
? Metals like Pt, Pd, Ni (elements of d block) form interstitial hydrides by 
absorbing large volume of hydrogen. Such hydrogen is called ‘occluded 
hydrogen and this property of adsorption of a gas by a metal is called occlusion.  
(iii) Reaction with metal oxides:-Hydrogen reduces oxides of less active metals to 
corresponding metal. 
Fe
3
O
4
  +  4H
2
3Fe  +  4H
2
O 
CuO  +  H
2
  Cu  +  H
2
O 
(iv) Reaction with non-metals:- 
3H
2 
(g) + N
2 
(g)                               ?2NH
3
(g)  { Haber process} 
H = - 92.6 kj/mole 
 
2H
2
 (g)+  O
2
 (g)  2H
2
OH = - 285.9 kj/mole 
 
(v) Reaction with carbon monoxide:- 
CO  +  H
2
                                     CH
3
OH 
(vi) Reaction with unsaturated Hydrocarbons:- 
(a) H
2
C = CH
2
  +  H
2
                                       H
3
C – CH
3 
(b) Hydroformylation of olefins to aldehydes:Hydroformilation or Oxo process
 
 RCH = CH
2
  +  H
2
  +  CO                                                    RCH
2
CH
2
CHO 
(c) Hydrogenation of oils:-Vegetable oils are polyun-saturated in nature. The C 
=C bonds in oils can easily undergo oxidation and the oil becomes rancid i.e., 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
112 
 
unpleasant in taste. Hydrogenation reduces the number of double bonds but 
completely. 
Vegetable Oil  +  H
2
                                   Fat (Solid) 
?Uses of Hydrogen:-it itused .. 
1. as a reducing agent. 
2. In the manufacture of vanaspati fat, ammonia, metal hydrides, methanol, 
fertilizers such as urea etc.  
3. In the manufacture of synthetic petrol. 
4. In the atomic hydrogen torch and oxy hydrogen torches for cutting and welding. 
Dihydrogen is dissociated with the help of an electric arc and the  
hydrogen atoms produced are allowed to recombine on the surface 
to be welded. High temperature of about 4000 k is generated.  
5. In the fuel cell for generating electrical energy. 
?Ortho and parahydrogens:-A molecules of dihydrogen …….abc 
 
 
 
? They show different physical properties. For example : 
(i) The thermal conductivity of para hydrogen is about 50 % greater than 
that of ortho hydrogen. 
(ii) The melting point of para hydrogen is 0.15 k below that of hydrogen 
containing 75% ortho hydrogen. 
? They show similar chemical properties. 
?Atomic hydrogen:- 
? Because of high H—H bond enthalpy, atomic hydrogen is produced only at 
high temp in an electric arc or under ultraviolet radiation. 
                        H
2
 (g)                                2H (g)                  H = + 435.9 kj 
                                                           (Atomic hydrogen) 
? Highly reactive.  
? Half life period is 0.3 sec and therefore, it immediately gets converted into the 
molecular form liberating a large amount of energy which is used for cutting 
and welding purposes.  
 
Ortho hydrogen
 
Para hydrogen
 
 
 
 
 
Page 5


109 
 
CHAPTER 9 
HYDROGEN 
? Position of Hydrogen in Periodic Table 
? Lightest element known having atomic number 1.  
? Dihydrogen 
? It resembles both alkali metals and halogens and therefore, its position is 
anomalous.  
? In modern periodic table it is located separately 
?Resemblance with alkali metals:- 
1.  Electronic configuration 
1
H = 1s
1
    11
Na = 1s
2
, 2s
2
, 2p
6
, 3s
1
    19
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
6
, 4s
1 
2. Electropositive character:  H
+
, Na
+
, K
+
 etc. 
3. Oxidation state:  +1 
4. Combination with electronegative elements: form binary compounds with 
electronegative elements like alkali metals. 
          Halides:  HClNaCl, KCletc 
Sulphides: H
2
S         Na
2
S, K
2
S     etc 
?Resemblance with halogens:- 
1. Electronic configuration: 
Both contain one electron less than the nearest noble gas configuration 
1
H = 1s
1
 (near to 
2
He) 
9
F = 1s
2
, 2s
2
, 2p
5 
(near to 
8
Ne) 
                         17
K = 1s
2
, 2s
2
, 2p
6
, 3s
2
3p
5 
(near to 
18
Ar) 
2. Non-metallic character: like halogens, hydrogen is non-metallic in nature.  
3. Atomicity: Diatomic molecules. 
4. Formation of similar types of compounds: 
i. Halides: CCl
4
, SiCl
4
, GeCl
4
 
ii. Hydrides: CH
4
, SiH
4
, GeH
4
 
5. Oxidation state:   –1 
      Na
+1
H
-1
                 Na
+1
Cl
-1
 
?Difference from alkali metals:- 
1) Ionization enthalpy: - the ionization enthalpy of hydrogen is very high in 
comparison to alkali metals. 
2) Non- metallic character: alkali metals are typical metals while hydrogen is 
non-metal 
3) Atomicity: hydrogen is diatomic while alkali metals are monoatomic. 
4) Nature of compounds: the compounds of hydrogen are predominantly 
covalent while those of alkali metals are ionic. For example: HCl is covalent 
while NaCl is ionic. 
The oxides of alkali metals are basic while hydrogen oxide is neutral.  
110 
 
?Difference from halogens:- 
1) Less tendency for hydride formation:Hydrogen has less tendency to take up 
electron to form hydride ion (H
-
) as compared to the halogens which from 
halide ions (X
-
) very easily. 
2) Absence of unshared pairs of electrons : 
3) Nature of oxides: The oxides of halogens are acidic while hydrogen oxide is 
neutral.  
 
? Occurrence of Hydrogen: 
? Hydrogen, the most abundant element in the universe and the third most 
abundant on the surface of the globe, is being visualised as the major future 
source of energy 
?Isotopes of hydrogen:- 
S.N. Property Protium Deuterium Tritium 
1 Relative abudance 99.985 % 0.015 % 10
-15
% 
2 Relative atomic mass 1.007825  2.014102  3.016 
3 Radioactive stability Non-
radioactive 
Non-
radioactive 
Radioactive  
t
1/2
 = 12.334 
yrs 
? Preparation: 
?Methods for commercial production of dihydrogen 
1. Electrolysis of water 
2H
2
O(l)                                           2H
2
(g)  O
2
(g) 
? The hydrogen prepared by this method is of very high purity. However, this 
method is not commonly used because it is very expensive. This method is can 
be used only at those places where the electricity is cheap.  
2. By the reaction of steam on coke :- 
C   +  H
2
O(g)           CO  + H
2
 
Water gas 
? Since the mixture of CO and H
2
 is used for the synthesis of methanol and a 
number of hydrocarbons, it is also called synthesis gas or syn gas. 
? The process of producing syn gas from coal or coke is called coal gasification.  
 
CO  +  H
2
  +  H
2
O                                        CO
2
  +  2H
2
 
Water gas      steam 
? This reaction is called water gas shift reaction. 
 
 
 
 
 
 
111 
 
?Properties of Hydrogen:- 
?Physical Properties:- 
1) It is slightly soluble in water (about 2 %) 
2) It is highly combustible and therefore should be handled carefully.  
3) It lightest substance. The weight of one litre hydrogen at NTP is only 0.0899 g. 
?Chemical properties:-Not very reactive due to high bond dissociation energy 
(435.88 kJ mol
-1
 at 298.2 K) 
(i)Combustion: - It burns with pale blue flame  
                    2H
2
 (g) + O
2
 (g)                                2H
2
O(l)
 
(ii) Reaction with metals:-Reactive metals like Na, K, Ca, Li and form hydrides. 
Ca  +  H
2
CaH
2
 
? Metals like Pt, Pd, Ni (elements of d block) form interstitial hydrides by 
absorbing large volume of hydrogen. Such hydrogen is called ‘occluded 
hydrogen and this property of adsorption of a gas by a metal is called occlusion.  
(iii) Reaction with metal oxides:-Hydrogen reduces oxides of less active metals to 
corresponding metal. 
Fe
3
O
4
  +  4H
2
3Fe  +  4H
2
O 
CuO  +  H
2
  Cu  +  H
2
O 
(iv) Reaction with non-metals:- 
3H
2 
(g) + N
2 
(g)                               ?2NH
3
(g)  { Haber process} 
H = - 92.6 kj/mole 
 
2H
2
 (g)+  O
2
 (g)  2H
2
OH = - 285.9 kj/mole 
 
(v) Reaction with carbon monoxide:- 
CO  +  H
2
                                     CH
3
OH 
(vi) Reaction with unsaturated Hydrocarbons:- 
(a) H
2
C = CH
2
  +  H
2
                                       H
3
C – CH
3 
(b) Hydroformylation of olefins to aldehydes:Hydroformilation or Oxo process
 
 RCH = CH
2
  +  H
2
  +  CO                                                    RCH
2
CH
2
CHO 
(c) Hydrogenation of oils:-Vegetable oils are polyun-saturated in nature. The C 
=C bonds in oils can easily undergo oxidation and the oil becomes rancid i.e., 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
112 
 
unpleasant in taste. Hydrogenation reduces the number of double bonds but 
completely. 
Vegetable Oil  +  H
2
                                   Fat (Solid) 
?Uses of Hydrogen:-it itused .. 
1. as a reducing agent. 
2. In the manufacture of vanaspati fat, ammonia, metal hydrides, methanol, 
fertilizers such as urea etc.  
3. In the manufacture of synthetic petrol. 
4. In the atomic hydrogen torch and oxy hydrogen torches for cutting and welding. 
Dihydrogen is dissociated with the help of an electric arc and the  
hydrogen atoms produced are allowed to recombine on the surface 
to be welded. High temperature of about 4000 k is generated.  
5. In the fuel cell for generating electrical energy. 
?Ortho and parahydrogens:-A molecules of dihydrogen …….abc 
 
 
 
? They show different physical properties. For example : 
(i) The thermal conductivity of para hydrogen is about 50 % greater than 
that of ortho hydrogen. 
(ii) The melting point of para hydrogen is 0.15 k below that of hydrogen 
containing 75% ortho hydrogen. 
? They show similar chemical properties. 
?Atomic hydrogen:- 
? Because of high H—H bond enthalpy, atomic hydrogen is produced only at 
high temp in an electric arc or under ultraviolet radiation. 
                        H
2
 (g)                                2H (g)                  H = + 435.9 kj 
                                                           (Atomic hydrogen) 
? Highly reactive.  
? Half life period is 0.3 sec and therefore, it immediately gets converted into the 
molecular form liberating a large amount of energy which is used for cutting 
and welding purposes.  
 
Ortho hydrogen
 
Para hydrogen
 
 
 
 
 
113 
 
?Nascent hydrogen:-The hydrogen produced in contact with the substance to be 
reduced is known as ‘nascent hydrogen’. It is very reactive form of hydrogenBetter 
reducing agent than ordinary dihydrogen. 
?Hydrides:-Under certain conditions H
2
 combines with almost all the elements ,except 
noble gases to form compounds called hydrides. 
? There are three types of hydrides ,they are 
          (i) Ionic or saline hydrides 
         (ii) Covalent or molecular hydrides (iii) Metallic or non-stoichiometric hydrides(i) 
Ionic or saline hydrides:- 
? These are the compounds of H
2
 formed with most of the s-block elements 
which are highly electro positive.  
(ii) Covalent or molecular hydrides:-These are the compounds of hydrogen 
formed with most of the p-block elements 
[a]Electron deficient:- The hydrides which do not have sufficient number of 
electrons to form normal covalent bonds is called electron deficient hydride. For 
example, hydride of group 13 (BH
3
, AlH
3
, etc.).They are known as Lewis acids 
i.e., electron acceptors. To make up their deficiency they generally exist in 
polymeric forms such as B
2
H
6
, Al
2
H
6
, etc. 
[b] Electron precise:-The hydrides which have sufficient number of electrons 
required for forming covalent bonds is called electron precise hydride. For 
example, hydrides of group 14 (CH
4
, SiH
4
, GeH
4
, SnH
4
, PbH
4
 etc.) they have 
tetrahedral geometry.  
[c] Electron rich hydrides:-The hydrides which have excess electrons as required 
to  form normal covalent bonds is called electron rich hydride. For example, 
hydrides of group 15 to 17 (NH
3
, PH
3
, H
2
O, H
2
S, H
2
Se, H
2
Te, HF etc.) 
(iii) Metallic or non-stoichiometric hydrides:- 
? These are formed by many d-block and f-block elements 
? These hydrides conducts heat and electricity though not efficient. 
?Water: -Water! It is the major part of all living organisms.water is also known 
as the river of life. 
? Human body has about 65%and some plants haveasmuch as 95%water. 
? STRUCTURE OF WATER:- 
? In a gas phase water is bent molecule with a bond angle of 104.5 and O-H bond 
length of 95.7pm It is highly polar molecule. 
 
 
 
Solid state 
 
O
H
H
104.5°
95.7 pm
 
O
H
H H
H
H
H
H
O O
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