Protium

Protium is the most common isotope of hydrogen, designated 1H. It consists of a single proton in the nucleus and a single orbiting electron, with no neutrons. In nature it accounts for the vast majority of hydrogen atoms; the remaining hydrogen atoms are mainly the heavier isotope, deuterium (2H), with trace amounts of tritium (3H).

Protium has an atomic mass of approximately 1.0078 u and an atomic number of 1. It forms diatomic molecules (H2) in all ordinary phases. Chemically, protium behaves like hydrogen in reactions, though physical properties and reaction rates can differ slightly from heavier isotopes due to isotopic mass (a phenomenon known as the kinetic isotope effect).

Occurrence and significance: Hydrogen is the most abundant element in the universe, and protium is its most common isotope. In natural water, protium predominates, while deuterium occurs in trace amounts and tritium is present only in very small quantities, often produced cosmogenically or in nuclear reactions.

Isolation, production, and uses: Pure protium is not usually isolated for everyday use; hydrogen gas is typically available containing mostly 1H. Enrichment or separation of isotopes is performed for specialized research, fusion experiments, or tracing studies. In spectroscopy, the 1H nucleus is used in proton (1H) nuclear magnetic resonance (NMR) to study molecular structure.

Safety: Hydrogen gas is highly flammable and forms potentially explosive mixtures with air, so handling requires appropriate precautions.