What is Hydrogen

Hydrogen is the smallest and lightest element in the universe among all the elements discovered so far. It has one electron and one proton. It has three isotopes, i.e protium, deuterium, and tritium. It is also an important part of many biomolecules like proteins, DNA, carbohydrates, etc. In nature, it is available as natural gas but in pure form, it is highly inflammable. In the modern periodic table, its position is not fixed because it belongs to s-block but its properties resemble the non-metals.

Hydrogen has various important real-life applications as mentioned below:

  • In petroleum refinery, it is used to remove sulfur content. In these plants, it is also used for hydroisomerization.

    Hydrogen example 

  • In ultraviolet lamps, it is used in the form of deuterium. These lamps on heating produce light in the ultraviolet region.

     ultraviolet lamps

  • One of the first use of hydrogen is its use in gas balloons. Due to its light weight, it is used for flying the hot balloons.

    hot balloons



Notes for Hydrogen

In this section, you will study about the important topics of the chapter, overview, formulae and some important tips and guidelines for the preparation of the chapter at the best.

Hydrogen- Important Topics

  • The position of Hydrogen in the periodic table
  • Isotopes of Hydrogen
  • Dihydrogen
  • Hydrides
  • Water
  • Hydrogen Peroxide
  • Dihydrogen as a fuel


Overview of the Chapter

Hydrogen is one of the important element in the universe. In nature, it exists in dihydrogen form as H2. In this article, you will study the various insights about this chapter and preparation tips.

The position of Hydrogen in the periodic table:

Hydrogen is placed in the first position of the periodic table. However, its actual position is always has been a matter of discussion in science. Its electronic configuration is 1s1, which means either it requires one more electron to completely fulfill the orbital or it can lose one electron. Thus Hydrogen behaves like alkali metals and halogens. Like alkali metals, Hydrogen forms halides, oxides, and sulphides. But in terms of ionization enthalpy, Hydrogen resembles more to halogens than alkali metals.

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Isotopes of Hydrogen:

As you all must know from your earlier classes, Hydrogen has three isotopes: protium, deuterium and tritium. Protium has no neutron, deuterium has 1 neutron and tritium has 2 neutrons. Since the electronic configuration of all these isotopes is same therefore chemical properties of these isotopes are same. However, their physical properties are considerably different from each other.

Dihydrogen is one of the most important chemicals in the universe. It is the most abundant element in the universe with almost 70% mass of the universe. In this section, you will study the preparation of dihydrogen, its properties, and uses.

  • Preparation:
    Hydrogen is prepared by the reaction of granulated zinc with hydrochloric acid or with aqueous alkali.
    \\*Zn\: +\: 2H^{+}\: \rightarrow \: Zn^{2+}\: H_{2}\\*Zn\: +\: 2NaOH\: \rightarrow \: Na_{2}ZnO_{2}\: +\: H_{2}

  • Properties of Dihydrogen
    (i) Physical properties:

    (a) It is colourless, tasteless, combustible gas.
    (b) It is almost 1/4 times lighter than air.
    (c) It is very low solubility in water.

(ii) Chemical Properties:
The bond dissociation enthalpy of dihydrogen is very high thus, it is very inert at room temperature.


  • Reaction with halogens:
    It reacts with halogens and forms hydrogen halides of the form HX.
    H_{2}(g)\: +\: X_{2}(g)\: \rightarrow\: 2HX(g)

  • Reaction with dioxygen:
    It reacts with dioxygen and forms water.
    2H_{2}(g)\: +\: O_{2}(g)\: \rightarrow\: 2H_{2}O(l)

  • Reaction with dinitrogen:
    It reacts with dinitrogen and forms ammonia:
    3H_{2}(g)\: +\: N_{2}(g)\: \rightarrow\: 2NH_{3}(g)

  • Reaction with metals:
    It reacts with metals and forms hydrides
    H_{2}(g)\: +\: 2M(g)\: \rightarrow\: 2MH(s)

  • Uses
    (i) It is used in the synthesis of ammonia.
    (ii) It is used in the manufacture of vanaspati fat.
    (iii) It is used in the production of metal hydrides.
    (iv) It is also used for the synthesis of hydrogen chloride.



Water is present on the earth in a tremendous amount. In the human body, it is available up to 70% and in some fruits like watermelon, it is present up to 96%. On earth, it is present in various forms as given in the table:






Saline lakes and inland seas


Polar ice and glaciers






Soil moisture


Atmospheric water vapour




Water has the bent structure with 104.50 bond angle and 2 lone pair of electrons on the oxygen atom. It is a highly polar molecule and forms hydrogen bonding with other water molecules. The structures of water are depicted in fig below:



Physical properties

  • It is a colourless liquid.
  • It's melting point is 0oC and boiling point is 100oC.
  • It is an excellent solvent for the transportation of ions and molecules.
  •  It has a high heat of vaporisation and high heat capacity.
  • It has higher specific heat, thermal conductivity, surface tension, etc.


Chemical properties

  • Amphoteric nature
    Water is amphoteric in nature. Thus it has the ability to act as an acid as well as a base.
  • Redox reactions with water
    Water is reduced very easily on reacting with highly electropositive metals.
    2H_{2}O(l)\: +\: 2Na(s)\: \rightarrow \: 2NaOH(aq)\: +\: H_{2}(g)
  • Hydrolysis reaction
    Some covalent and ionic compounds are hydrolysed in water.
    \mathrm{P_{4}O_{10}(s)\, +\, 6H_{2}O(l)\, \rightarrow \, 4H_{3}PO_{4}(aq)}

Hard and Soft Water
When salts of calcium and magnesium are dissolved in the water then it is called as hard water, but when these salts are not present in the water then it is known as soft water. Hard water does not form lather with soaps but soft water forms lather. For washing in hard water, soaps are not efficient and thus we use detergents. With proper water treatment, this hardness of water can be removed. 

Hydrogen Peroxide(H2O2)
Hydrogen peroxide is one of the most important compound which is used in the pollution control treatment. Some of the important physical properties of hydrogen peroxide are given in the table as below:

Melting Point(K)


Boiling Point(K)


Vapour pressure




Dielectric Constant


Electrical Conductivity



  • Preparation: Hydrogen peroxide is prepared by the following methods as discussed below:
    (i) In this method, barium peroxide is treated with sulphuric acid and thus form barium sulphate and hydrogen peroxide.

    \mathrm{BaO_{2}.8H_{2}O(s)\: +\: H_{2}SO_{4}(aq)\: \rightarrow\: BaSO_{4}(s)\: +\: H_{2}O_{2}(aq)\: +\: 8H_{2}O(l)}

    (ii) In this method, with the help of electrolytic oxidation of acidified sulfate solutions, peroxodisulphate is obtained. This peroxodisulphate is then hydrolyzed to yield hydrogen peroxide.

    \mathrm{2HSO_{4}^{-}(aq)\, \overset{Electrolysis}{\rightarrow}\, HO_{3}SOOSO_{3}H(aq)\overset{Hydrolysis}{\rightarrow}\, 2HSO_{4}^{-}(aq)\, +\, 2H^{+}(aq)\, +\, H_{2}O_{2}}


  • Uses
    (i) In daily life, hydrogen peroxide is used as a hair bleach.
    (ii) It is used in the synthesis of tartaric acid and some food products.
    (iii) It is used a bleaching agent for textiles, leather, fats,etc.
    (iv) It is used to manufacture chemicals like sodium perborate and per-carbonate.


Dihydrogen as a fuel

Dihydrogen can be used fuel as on combustion it produces a tremendous amount of heat. The combustion of dihydrogen can produce almost three the energy as produced by petrol. Also, the pollutants released are also lesser than petrol. The only pollutant from dihydrogen released is oxides of dinitrogen, but this problem can be solved very easily by using a little amount of water. This addition of water will reduce the temperature and thus the reaction between nitrogen and oxygen will not take place. 
But using dihydrogen gas as a fuel has some limitations. The cylinder of compressed dihydrogen gas weighs almost 30 times heavier than a petrol tank. Also, converting dihydrogen to the liquid state requires cooling to 20K. Thus it requires expensive insulated tanks.


How to prepare for Hydrogen?

  • This chapter is a part of inorganic chemistry. It is completely theory-based and very easy to learn, there is no need to memorize any formula. 

  • Before reading this chapter, first, you must have the basic knowledge of chapter - periodic classification of elements.

  • Rest this complete chapter is very simple, just be regular and be consistent in your numerical practice. 


Prescribed Books

First, you must finish the class XI and XII NCERT textbook and solve each and every example and unsolved question given in it. Then for advanced level preparation like JEE and NEET, you must follow O.P. Tandon. You must definitely solve the previous year papers. Meanwhile, in the preparation, you must continuously give the mock tests for the depth of knowledge. Our platform will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.


Chemistry Chapter- wise Notes for Engineering and Medical Exams

Chapters No.

Chapters Name

Chapter 1

Some basic concepts in chemistry

Chapter 2

States of matter

Chapter 3

Atomic Structure

Chapter 4


Chapter 5

Chemical Thermodynamics

Chapter 6


Chapter 7

Redox Reaction and Electrochemistry

Chapter 8

Chemical kinetics

Chapter 9

Surface Chemistry

Chapter 10

General Principle and processes of Isolation of metals

Chapter 11

Classification of Elements and Periodic table

Chapter 13

p- block Elements

Chapter 14 

s-block Elements (Alkali and Alkaline Earth Metals)

Chapter 15 

Chemical Bonding and Molecular Structure

Chapter 16


Chapter 17

Coordination Compounds

Chapter 18 

Environmental Chemistry

Chapter 19

Purification and Characterisation of Organic Compounds

Chapter 20

Some Basic Principles of Organic Chemistry

Chapter 21


Chapter 22

Organic Compounds containing Halogens

Chapter 23

Organic Compounds containing Oxygen

Chapter 24

Organic Compounds Containing Nitrogen

Chapter 25


Chapter 26


Chapter 27

Chemistry in Everyday Life

Chapter 28

Principles Related to Practical Chemistry

Topics from Hydrogen

  • Position of hydrogen in periodic table, ( JEE Main ) (2 concepts)
  • isotopes ( JEE Main ) (1 concepts)
  • preparation, properties and uses of hydrogen ( JEE Main ) (15 concepts)
  • Classification of hydrides - ionic, covalent and interstitial ( JEE Main ) (7 concepts)
  • Physical and chemical properties of water and heavy water ( JEE Main ) (7 concepts)
  • Structure, preparation, reactions and uses of hydrogen peroxide ( JEE Main ) (12 concepts)
  • PREPARATION OF DIHYDROGEN, H2 ( JEE Main ) (1 concepts)
  • PROPERTIES OF DIHYDROGEN ( JEE Main ) (4 concepts)
  • HYDRIDES ( JEE Main ) (2 concepts)
  • HYDROGEN PEROXIDE (H2O2) ( JEE Main ) (7 concepts)
  • WATER ( JEE Main ) (4 concepts)

Important Books for Hydrogen

  • Hydrogen Book
  • Hydrogen Book