According to the CBSE Syllabus 2023-24, this chapter has been removed from NCERT Class 11 Chemistry textbook.

The lightest atom on earth is hydrogen which has a single electron. In the year 1766, Henry Cavendish was the first to discover it. The three stable isotopes of hydrogen are protium, deuterium, and tritium. The radioactive isotope among these three is tritium. Hydrogen is one of the most abundant elements found in the universe. Even though it resembles halogen and alkali metals, it has unique properties and has a separate position in the periodic table.

Water-Gas Shift Reaction

On an industrial scale level, Dihydrogen is prepared from petrochemicals by water-gas shift reaction. It is got in the form of a byproduct of the electrolysis of brine.

Also Read: Preparation Of Hydrogen And Uses

Bond Dissociation Enthalpy

Dihydrogen has the highest H-H bond dissociation enthalpy for a single bond between the two atoms. The H-H bond dissociation enthalpy equals 435.88 kJ mol^–1

Read More: Bond Dissociation Enthalpy

Hydrides

Due to high negative dissociation enthalpy, dihydrogen is inactive at room temperature.  At suitable conditions, dihydrogen can combine with all the possible elements to form hydrides.

There are three different ways to categorize the hydride:

• Saline or Ionic hydrides – Good reagent to prepare additional hydride compounds
• Molecular or Covalent hydrides – Important for daily life. Example H₂O
• Non-stoichiometric or metallic hydrides – Used for ultra-purification of dihydrogen

Read More: Hydrides

Important Questions

1. How can you increase the production of dihydrogen from coal gasification?
2. Explain the auto-protolysis of water along with its significance.
3. Explain the amphoteric nature of water with chemical reactions.
4. Distinguish between hydration and hydrolysis.

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Other Important Links:

• Hydrogen – Overview
• Isotopes of Hydrogen
• Isotopes and Isobars