1H

1H, also known as hydrogen-1 or protium, is the most common isotope of hydrogen. Its nucleus consists of a single proton and no neutrons, and it is a stable, non-radioactive isotope. The element hydrogen has atomic number 1, and a mass number of 1 for this isotope. In atomic terms, protium is the lightest and simplest nucleus.

Nuclear and physical properties

The 1H nucleus has spin 1/2, giving rise to a magnetic moment that makes it highly useful in spectroscopy and magnetic resonance techniques. Its atomic mass is about 1.0078 unified atomic mass units (u). Protium participates in a wide range of chemical bonds, most notably forming H2 gas when two 1H nuclei share electrons. The ionization energy of hydrogen is about 13.6 eV, and in nature this isotope is essentially non-radioactive, unlike its heavier isotopes deuterium (2H) and tritium (3H).

Natural abundance and significance

On Earth, about 99.98% of naturally occurring hydrogen is 1H, with deuterium (2H) making up roughly 0.015% and tritium (3H) present only in trace amounts. In the universe, hydrogen-1 is the predominant isotope and the primary fuel in stellar fusion processes, especially in the proton–proton chain that powers stars like the Sun. Its abundance and simple structure make it central to fields ranging from chemistry and spectroscopy to astrophysics and cosmology.

Common applications and related isotopes

1H is the standard reference nucleus in nuclear magnetic resonance (NMR) spectroscopy and in magnetic resonance imaging (MRI). Isotopic labeling with deuterium (2H) or tritium (3H) is widely used to study reaction mechanisms and biological processes, highlighting the distinct properties of hydrogen’s isotopes.

See also: Deuterium (2H), Tritium (3H), isotope.