On the periodic table, which element has the atomic number 1?

On the periodic table, hydrogen is the element with atomic number 1. Its atomic number means that every neutral hydrogen atom has one proton in its nucleus.

Hydrogen is the lightest and most abundant chemical element in the universe. A normal hydrogen atom contains one proton and one electron, but its most common isotope has no neutron. Hydrogen is represented by the symbol H and usually exists as the diatomic molecule H₂.

Hydrogen was recognized as a distinct substance in the 18th century. Henry Cavendish identified it as a gas that produced water when burned, while Antoine Lavoisier later gave it the name hydrogen, derived from Greek roots meaning “water-former.”

Hydrogen is often placed above the alkali metals because it has one valence electron, but it is not an alkali metal. It behaves differently from that group and is generally treated as a unique element.