Hydrogen - Notes, Topics, Books, FAQs

Important Topics of Hydrogen

Isotopes of Hydrogen:

Hydrogen has three key isotopes—protium (¹H), deuterium (²H or D), and tritium (³H or T). All three share the same single-electron configuration but differ in neutron count: protium has none, deuterium has one, and tritium has two neutrons. Tritium is the only radioactive isotope of hydrogen

Dihydrogen:

Dihydrogen is a colorless, odorless, and tasteless gas that burns readily. It is lighter than air and does not dissolve in water. Since hydrogen’s electronegativity falls between that of metals and non-metals, it can behave both as an electron donor (electropositive) and an electron acceptor (electronegative).

Hydrides:

Hydrides are compounds in which hydrogen is chemically bonded to an element that is more electropositive. These substances usually appear as colorless or grayish crystalline solids and are characterized by high melting and boiling points.

1. Ionic (Saline) Hydrides

   • Formed by reaction of hydrogen with highly electropositive metals (usually s-block).

   • Example: NaH, CaH₂

   • Nature: Ionic (H⁻)

   • Properties:

     • High melting point

     • Reacts with water to liberate hydrogen gas:

       $\mathrm{CaH}_2+2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{OH})_2+2 \mathrm{H}_2$​

2. Covalent (Molecular) Hydrides

   • Formed by reaction of hydrogen with p-block elements.

   • Example: CH₄, NH₃, HCl

   • Nature: Covalent

   • Properties:

     • Low melting and boiling points

     • Usually gases at room temperature

3. Metallic (Interstitial) Hydrides

   • Formed by reaction of hydrogen with transition metals.

   • Example: TiH₁.₈, VH₀.₈

   • Nature: Hydrogen occupies interstitial spaces in the metal lattice.

   • Properties:

     • High melting point

     • Conducts electricity

     • Usually non-stoichiometric

Importance Of Water (H₂O):

Water is known for having solvent capabilities, and colloquially it is often called the "universal solvent" because it dissolves more substances than any other liquid. Water is neutral in nature. pH of the pure water is 7. It is a weak electrolyte and ionizes into H⁺ and OH^- ions.

Hard Water And Soft Water:

When water has a high concentration of dissolved minerals—mostly calcium and magnesium and when it produces sufficient lather with soap that is called Hard Water And Soft Water respectively.

Hydrogen Peroxide:

Hydrogen Peroxide has a formula H₂O_{2 ,} it is a colorless, unstable, and highly reactive liquid at room temperature. It is also an important chemical used in pollution control treatment of domestic and industrial effluents.

Various Important Real-life Applications Of Hydrogen:

• In petroleum refineries, it is used to remove sulfur content. In these plants, it is also used for hydroisomerization.
  
• In ultraviolet lamps, it is used in the form of deuterium. These lamps on heating produce light in the ultraviolet region.
  
• One of the first uses of hydrogen is its use in gas balloons. Due to its light weight, it is used for flying hot balloons.
  

Overview Of The Chapter

Hydrogen is the simplest and lightest element, commonly found as diatomic H₂ gas. It has three isotopes—protium (¹H), deuterium (²H), and radioactive tritium (³H)—which differ only in their neutron count. H₂ is colorless, odorless, tasteless, flammable, lighter than air, and barely dissolves in water. It’s produced in labs (such as by reacting zinc with acid) and on an industrial scale using methods like electrolysis or steam reforming. Hydrogen forms ionic, covalent, and metallic hydrides and is widely used in making ammonia and methanol, hydrogenating oils, reducing metal oxides, fueling rockets and fuel cells, and welding. 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 s orbital or it can lose one electron. Thus Hydrogen behaves like alkali metals and halogens. Like alkali metals, Hydrogen forms halides, oxides, and sulfides. But in terms of ionization enthalpy, Hydrogen resembles more to halogens than alkali metals.

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
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.

Hydrides

Water
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:

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 0^oC and boiling point is 100^oC.
• It is an excellent solvent for the transportation of ions and molecules.
• It has a high heat of vaporization 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 compounds which is used in pollution control treatment. Some of the important physical properties of hydrogen peroxide are given in the table below:

• 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

Hydrogen gas burns with a high energy output, producing nearly three times the energy of petrol per unit mass. It emits fewer pollutants, with nitrogen oxides being the primary byproduct. This issue can be mitigated by introducing water into the combustion process, lowering the temperature and reducing nitrogen oxide formation.

However, using hydrogen as a fuel presents challenges. Compressed hydrogen cylinders are significantly heavier than petrol tanks, approximately 30 times more. Additionally, liquefying hydrogen requires cooling it to around 20 K, necessitating expensive, insulated storage tanks.

How To Prepare For Hydrogen?

• Understand the Basics
  Before diving into this chapter, ensure you're familiar with the "Periodic Classification of Elements" as it provides foundational knowledge essential for understanding hydrogen's position and behavior.

• Focus on Theory
  This chapter is entirely theory-based, making it relatively straightforward. There's no need to memorize complex formulas; instead, concentrate on grasping the concepts and their applications.

• Practice Regularly
  While the chapter is theory-heavy, practicing related numerical problems can enhance your understanding and retention of the material.

• Stay Consistent
  Regular study sessions, even if brief, can be more effective than cramming. Consistency helps reinforce learning and improves long-term retention.

• Use Visual Aids
  Diagrams, charts, and tables can aid in better understanding and memorization of key concepts, such as the preparation methods and properties of hydrogen.

• Clarify Doubts Promptly
  Don't hesitate to ask teachers or peers about concepts you find challenging. Clearing doubts promptly ensures a solid grasp of the subject matter.

• Relate to Real-World Applications
  Understanding the practical applications of hydrogen, like its use in fuel cells or the Haber process, can make the theoretical concepts more relatable and easier to comprehend.

Also Read,

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's papers. Meanwhile, in the preparation, you must continuously give the mock tests for the depth of knowledge. Our platform will help you with a variety of questions for deeper knowledge with the help of videos, articles and mock tests.

Previous Year Questions Of Hydrogen

Question 1: $\mathrm{O}-\mathrm{O}$ bond length in $\mathrm{H}_2 \mathrm{O}_2$ is $\underline{\mathrm{X}}$ than the $\mathrm{O}-\mathrm{O}$ bond length in $\mathrm{F}_2 \mathrm{O}_2$. The $\mathrm{O}-\mathrm{H}$ bond length in $\mathrm{H}_2 \mathrm{O}_2$ is $\underline{Y}$ than that of the $\mathrm{O}-\mathrm{F}$ bond in $\mathrm{F}_2 \mathrm{O}_2$.
Choose the correct option for $X$ and $Y$ from those given below:

1) X-shorter, Y -longer

2) X-shorter, Y-shorter

3) X-longer, Y-shorter

4) X-longer, Y-longer

Solution:

$\rightarrow(\mathrm{O}-\mathrm{O}) \mathrm{BL}$ in $\mathrm{H}_2 \mathrm{O}_2$ in longer then $(\mathrm{O}-\mathrm{O}) \mathrm{BL}$ in $\mathrm{O}_2 \mathrm{~F}_2$
$\rightarrow(\mathrm{O}-\mathrm{H}) \mathrm{BL}$ in $\mathrm{H}_2 \mathrm{O}_2$ in shorter than $(\mathrm{O}-\mathrm{F}) \mathrm{BL}$ in $\mathrm{O}_2 \mathrm{~F}_2$
Hence, the answer is the option (3).

Question 2: Which of the following silicates are used as ion exchangers in softening of hard water:

1) Orthosilicate

2) Zeolite

3) Cyclic silicate

4) Chain silicate

Solution:

Zeolites are 3-D silicates. These are used as ion exchangers in softening of hard water common zeolite is sodium aluminosilicate.

Hence, the answer is option (2).

Question 3: Which of the following statements is correct?
(i) Metallic hydrides are deficient of Hydrogen.
(ii) Metallic hydrides conduct heat and electricity.
(iii) Ionic hydrides do not conduct electricity in solid-state.
(iv) Ionic hydrides are very good conductors of electricity in solid-state.

1) (i), (iii), and (iv)

2) (ii), (iii), and (iv)

3) (i), (ii), and (iii)

4) (i), (ii), and (iv)

Solution:

The answer is the option (i), (ii), and (iii) Metallic hydrides are deficient of Hydrogen, Metallic hydrides conduct heat and electricity, and Ionic hydrides do not conduct electricity in solid-state.

Hydride and not volatile or conductive in the solid-state but are crystalline instead. While metallic hydrides are non-stoichiometric hydrides. They only conduct electricity in their molten state.

Hence, the answer is the option (3).

Practice more questions from the link given below:

Conclusion

Hydrogen is the simplest element, made of one proton and one electron, and has three isotopes: protium, deuterium, and tritium. It normally exists as diatomic H₂ gas, which has two nuclear spin forms (ortho and para) and shows traits of both alkali metals and halogens. Hydrogen is prepared in labs (e.g., metal-acid reactions) and industrially (steam reforming). It forms ionic, covalent, and metallic hydrides. Key uses include manufacturing ammonia and methanol, hydrogenating oils, reducing metal oxides, fuel cells, rockets, welding, and supporting water and hydrogen peroxide chemistry.