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 (ยนH or H): 1 proton, 0 neutrons, 1 electron. Most abundant (~99.985%).
- Deuterium (ยฒH or D): 1 proton, 1 neutron, 1 electron. Also called heavy hydrogen. Abundance โ 0.015%.
- Tritium (ยณH or T): 1 proton, 2 neutrons, 1 electron. Least abundant (โ 10โปยนโธ%), 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 โ _2^3 He + _-1^0 ฮฒ_1^3 H: Tritium nucleus_2^3 He: Helium-3 nucleus_-1^0 ฮฒ: 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.