Isotopes of Hydrogen

Isotopes are other derived variants of the same chemical element, which differ in the number of neutrons and, eventually, nucleon numbers. Isotopes of any particular chemical element have similar proton composition but different numbers of neutrons in each atom. The ‘Atomic number’ of an element is denoted by the number of protons present in the atomic nucleus. The number of nucleons (Both protons and neutrons) in the atomic nucleus directly refers to the ‘Atomic mass number’ i.e. 

Z (Atomic number/Proton number) + N (Neutron number) = Atomic Mass number.

An Example: Carbon has an atomic number of 6, which means that every carbon atom has a proton count of 6.  

Carbon-12, Carbon-13 and carbon-14 are its isotopes. 12, 13, 14 are the mass numbers of these three isotopes respectively which means:

1st isotope - Carbon-12: (Z=6) +(N=6)

2nd isotope - Carbon-13: (Z=6) +(N=7)

3rd isotope - Carbon-13: (Z=6) +(N=8)

The isotopes of every element have a different mass number. The proton count remains constant, whereas the neutron count changes, which further marks a change in the Isotopes. Thus, elements having similar atomic numbers and different mass numbers are Isotopes. 

Hydrogen is the first chemical element with an atomic number of 1. It is the lightest element with a standard atomic weight of 1.008 in the periodic table. It’s a highly combustible diatomic gas with the molecular formula H2. It can exist in different states such as gaseous, liquid, slush, solid, and metallic hydrogen. Owing to standard temperature and pressure, hydrogen is colourless, tasteless, and devoid of any odour. It is equipped with covalent compounds with several non-metallic elements. This is the same reason why most of it exists in molecular forms on the planet in the form of water or organic compounds. 

What are the Isotopes of Hydrogen? 

Hydrogen has three naturally occurring Isotopes: Protium (1H), Deuterium(2H) and Tritium(3H). Scientists and researchers have enumerated four other isotopes, i.e., 4H to 7H, but these isotopes are unstable and do not exist in natural forms. Such isotopes are synthetic and have an average lifetime lesser than a zeptosecond, i.e., 10-21 seconds.

Protium and Deuterium are classified under the stable isotopes of hydrogen. Tritium is a stable radioactive isotope or ‘radioisotope’ of hydrogen, and it has a half-life of about 12.3 years. Among the other heavier isotopes of hydrogen, 5H is the most stable, and 7H is the minimum stable. 

The International Union of Pure and Applied Chemistry or IUPAC advocates the usage of standard Isotopic symbols to avoid complications while working out chemical formulas. 

Protium or 1H is the most common isotope of Hydrogen, and its nucleus consists of only 1 proton, i.e., it’s atomic number = mass number. It’s generally found in the molecular formula of H2. This diatomic gas is highly reactive, combustible, and easy to combine with other atoms of different compounds because monoatomic hydrogen almost does not exist. 

The H-H bond is the most durable bond found in the planet with a natural abundance of 99.8%. It dissociates to a very minimum extent until high temperatures are reached. The H-H bond has a dissociation energy of 435.8 kj/mol at 298K, which depicts the strength of the respective chemical bond. The average mass of protium is 1.007825 amu. 

Several new theories on Particle physics anticipates that a proton can decay, though the process is prolonged. 

Deuterium or 2H is another stable isotope of hydrogen. Deuterium was prepared in pure form by the Electrolytic method of concentration. The nucleus of Deuterium, also known as ‘Deuteron,’ consists of 1 proton and one neutron, i.e., Mass number=2; whereas, protium has no neutron count in its nucleus. Because of this, Deuterium is roughly double the mass of protium, i.e., 2.014102 amu. Deuterium is generally found in traceable amounts in the form of natural deuterium gas or D2. 

It is naturally available in the universe bonded with protium 1H atoms, forming a gas called Hydrogen deuteride or 1H2H or only HD. Its natural availability also accounts for nearly 0.0156% of all hydrogen found on the planet; hence it is not radioactive. 

Deuterium enriched molecules in water instead of normal hydrogen is known as ‘Heavy Hydrogen’ (D2O) or ‘Deuterium Oxide,’ which is approximately 10.6% denser than regular water. 

Though it is not radioactive, it does not show any significant toxicity hazard in human beings. However, it can still be slightly toxic for multicellular eukaryotic animals, causing a 25% replacement of body water. That can further cause significant problems in cell division. It can also cause death by bone marrow failure and gastrointestinal lining failure, alternatively known as ‘Cytotoxic syndrome.’ 

Deuterium can also be obtained in its concentrated form by the fractional distillation of water. Chemical bonds made up of Deuterium and Tritium can make comparatively stronger bonds than protium. These differences are enough to bring changes in biological reactions. 

Applications of Deuterium: 

  • ‘Heavy water’ is alternatively used as a neutron moderator 

  • as a coolant for nuclear reactors. 

  • It can work as a prospective fuel for nuclear fusion, amateur fusors and neutron generators. 

  • It is also used in prototype fusion reactors.

  • NMR spectroscopy

Tritium or 3H was prepared for the first time in 1935 by bombarding Deuterium with high energy deuterons i.e. 

                 2D+ 2D 1H+ 3T

It is one of the most stable radioisotopes of hydrogen. It comprises one proton and two neutrons in its nucleus. According to scientific predictions, Tritium can decay into very light (low energy) negative beta particles, and it changes itself into helium-3. It is present in very minute proportions in natural water. 

It is continuously formed in the upper atmosphere by nuclear reactions by cosmic rays and interaction with atmospheric gases. Cosmic rays, which mostly consist of high-energy protons, react with nitrogen atoms to form neutrons. These neutrons further react with more nitrogen atoms to form Tritium, and this naturally formed Tritium reaches the surface of the earth in the form of rain.  

Applications of Tritium:

  • making of luminous paints

  • used as a radiolabel in biological labelling experiments, 

  • self-powered lighting devices or radio luminescent light sources 

  • used as a radioactive tracer

  • in beta, voltaic devices to create the atomic batter for energy production

  • Used in oceanic transient tracer

  • Used in hydrogen bomb secondaries. 

Heavier Synthetic Isotopes:

4H or Hydrogen-4 consists of one proton and three neutrons in its nucleus. It is obtained by bombarding Tritium with fast-moving deuterium nuclei or deuterons. Its presence was found by detecting the emitted photons. It decays through neutron emission into Hydrogen-3. It is a highly unstable isotope of Hydrogen. 

5H or Hydrogen-5 is another unstable isotope of hydrogen. Its nucleus consists of a single proton and four neutrons. It has been synthesized or acquired by bombarding Tritium with fast-moving tritium nuclei. It is capable of decaying through double neutron emission into Hydrogen-3. It has a half-life of 910 yoctoseconds.  

6H or Hydrogen-6 decays through triple or quadruple neutron emission into Hydrogen-2. It has a half-life of 290 yoctoseconds. It's highly unstable, almost obsolete.

7H or Hydrogen-7 consists of 1 proton and six neutrons. It was obtained by bombarding hydrogen with helium-8 atoms. It has a half-life of 23 yoctoseconds.

FAQ (Frequently Asked Questions)

1. Which is the most Common Isotope of Hydrogen?

Protium is the most common isotope of hydrogen. Its atomic number is equal to its mass number. It accounts for nearly 99% of universal hydrogen.

2. Which is the most Radioactive Isotope of Hydrogen?

Tritium is the most radioactive isotope of Hydrogen. It can be used in radioluminescent light sources.

3. What is Heavy Hydrogen?

Heavy hydrogen is basically ‘Deuterium oxide’ or D2O. It is ten times denser than normal water. Deuterium enriched molecules in water instead of normal hydrogen is called Heavy hydrogen. It does not have any radioactive properties. Thus, it’s not toxic.

4. What is the Atomic Mass of Deuterium?

The mass of Deuterium is 2.014 amu which is double the mass of protium.

5. What are Heavier Synthetic Isotopes?

Heavier synthetic isotopes consist of unstable isotopes of Hydrogen, i.e. 4H, 5H, 6H, 7H.