Isotopes of Hydrogen for NEET: Key Properties & MCQs
Isotopes of HydrogenHydrogen ChapterNEET ChemistryNEET 2025ProtiumDeuteriumTritium
Isotopes of Hydrogen for NEET: Key Properties & MCQs
Hydrogen·2 min read·NEET 2026
What NEET Asks
Questions on the definition and distinguishing features of hydrogen isotopes (proton/neutron count).
Comparisons of physical properties (e.g., boiling point, density) and chemical properties (e.g., reaction rates, bond strength).
Relative abundance and the radioactive nature of tritium are frequently tested concepts.
Key Points
Isotopes are atoms of the same element with the same atomic number but different mass numbers (different number of neutrons).
Protium (¹H or H): 1 proton, 0 neutrons, 1 electron. Most abundant (~99.985%).
Deuterium (²H or D): 1 proton, 1 neutron, 1 electron. Also called heavy hydrogen. Abundance ≈ 0.015%.
Tritium (³H or T): 1 proton, 2 neutrons, 1 electron. Least abundant (≈ 10⁻¹⁸%), radioactive (beta emitter).
Physical Properties: Deuterium and Tritium compounds have higher melting points, boiling points, density, and enthalpy of fusion/vaporization than Protium compounds due to larger mass and stronger intermolecular forces.
Chemical Properties: Due to the kinetic isotope effect, heavier isotopes react slower. Bond dissociation energy follows T-H > D-H > H-H.
Must-Know Formula / Reaction
Tritium Beta Decay:_1^3 H → _2^3 He + _-1^0 β
_1^3 H: Tritium nucleus
_2^3 He: Helium-3 nucleus
_-1^0 β: Beta particle (electron) emitted
Common Mistakes
Students often confuse the number of neutrons in Protium (0) with deuterium (1) or tritium (2).
Don't forget that Tritium is the ONLY radioactive isotope among the three, undergoing beta decay.
Underestimating the impact of mass difference on physical properties (like boiling point) and chemical reaction rates.
Rapid Revision
Remember: Protium (0 neutrons, most abundant), Deuterium (1 neutron, heavy water), Tritium (2 neutrons, radioactive beta emitter, least abundant). Heavier isotopes have higher physical property values and react slower.
Frequently Asked Questions
What are the isotopes of hydrogen?▾
Hydrogen has three main isotopes: Protium (¹H), Deuterium (²H), and Tritium (³H). They all have one proton and one electron but differ in the number of neutrons, leading to different mass numbers.
How do Protium, Deuterium, and Tritium differ in properties?▾
Protium has 0 neutrons, Deuterium has 1 neutron, and Tritium has 2 neutrons. This mass difference leads to varying physical properties (e.g., boiling point, density increase with mass) and chemical reaction rates (heavier isotopes react slower). Tritium is also unique for being radioactive.
Why is Tritium radioactive, and what kind of decay does it undergo?▾
Tritium is radioactive because its nucleus with two neutrons and one proton is unstable. It undergoes beta decay, where a neutron converts into a proton, emitting an electron (beta particle) and transforming into Helium-3.
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