Isotopes of Hydrogen

Isotopes of an element are defined as different members of the family of that element having the same number of protons but different neutrons. The hydrogen atom is said to have the simplest nucleus – containing one proton. It has one negatively charged electron in its shell. Its atomic number is 1, and mostly, the mass number is also taken to be 1. However, the mass number can also be 2 and 3, depending on the number of neutrons in the nucleus. Neutrons are neutral subatomic particles that determine the mass number of an atom.  

Table 1: Isotopes of Hydrogen chart

 Hydrogen is the only element in chemistry whose isotopes are referred to by different names.

Hydrogen or Protium

This is the most commonly found isotope of hydrogen, with an abundance of over 99.98%. This means that the rest of the two isotopes exist only in trace amounts in nature. Naturally, it exists in the form of dihydrogen gas or H2. This is a highly stable isotope whose decay has never been observed.

Whatever hydrogen is used in everyday life and industrially, it is the protium isotope only. It has several applications in fuel cells, mining, chemical syntheses of various compounds, etc. The easiest way to obtain protium is by hydrolysis of water. 

2H2O → 2H2 + O2 

Deuterium

Deuterium is the isotope of hydrogen with mass number 2. It has 1 proton and 1 neutron in its nucleus. Its nucleus is known as the deuteron. It is represented by 21H or D. Its percentage abundance is a little over 0.015%. The additional neutron in the nucleus makes it twice as heavier as the more commonly found isotope protium. It is stable, but not as much as protium.

In nature, it exists most commonly as HD or hydrogen deuteride, in which deuterium is singly bonded with protium. In its pure form, it exists as D2, but only in trace amounts.

Just like hydrogen, it is very reactive and forms chemical compounds very similar to that of protium. It forms stronger bonds than protium. However, the reaction rate or the spontaneity with which it reacts is lower because of a higher mass. This property makes it useful as an isotopic tracer in hydrogen-containing chemical and biochemical reactions. Isotopic tracer.

Heavy Water: D2O or deuterium oxide is somewhat analogous to water and is referred to as heavy water. Its density is 10.6% more than that of regular water (H2O), and it is more viscous also. Deuterium is not a radioactive material and not toxic to humans as such when present in small concentrations. However, if 25% of our body’s water is replaced by heavy water, it would pose numerous health problems like sterility and cell division issues. If 50% water is replaced, then the person would die because of the cytotoxic syndrome in which the bone marrow fails, and the gastrointestinal lining is damaged.

There are very minute amounts of heavy water in regular water, and thus heavy water can be obtained by repeated fractional distillation of an extremely large volume of water.

Uses of Deuterium

Heavy water is used as a coolant in nuclear reactors. It slows down fast-approaching neutrons and thus helps control the nuclear reactions in power plants. 

It is also used in NMR (Nuclear Magnetic Resonance) studies. It is used as a solvent when we want to detect the signals of normal hydrogen. Protium has different spectroscopic behaviour, and thus only it is detected, whereas deuterium acts as a desirable solvent whose signals do not show up in the spectra.

Tritium

is represented by 31H or T. It is highly radioactive, and its mass is triple of hydrogen. It has two neutrons and one proton. It has a half-life of 12.32 years, and it decays into He-3 (helium with mass number 3) via 𝛽-decay.

Tritium is formed alongside helium upon the nuclear reaction between Li-6 and a neutron. Hence, it is a byproduct of nuclear reactions.

 6Li + 1n → 4He + T

The first preparation of tritium was in 1935 by the collision of two deuterium atoms together. 

2D + 2D → 1H + 3T

It is found in extremely low (almost negligible) concentrations in regular water. High energy cosmic rays from the sun react with atmospheric gases like nitrogen to form tritium. This tritium formed at high altitude comes down to the earth’s surface by mixing in rainwater.

It is used in nuclear fusion reactions, as an isotopic tracer, and in self-powered lighting devices. It is used in luminous paints. It is used to make luminous dials and in safety signs that are visible at night. It finds applications in animal metabolism research studies as well.

Conclusion 

From the isotopes of the hydrogen chart, three naturally found isotopes, namely hydrogen or protium, deuterium, and tritium, can be seen. Protium is the most abundant and most stable. Tritium is the heaviest of them all and least stable, making it radioactive. The H-2 and H-3 isotopes of hydrogen are used in nuclear reactors. They differ from each other in terms of mass number and chemical reactivity. There are other isotopes of hydrogen as well with even higher mass numbers that have been synthesised synthetically, but they have unusually low half-lives.