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Hydrogen (H), element 1
Hydrogen (H) is the chemical element with atomic number 1: a nonmetal in group 1, period 1. At 25 °C it is a gas, with an atomic mass of 1.008 u. It melts at -259.34 °C, one of the 3 lowest melting points known.
Physical and chemical data
| Atomic number | 1 |
|---|---|
| Symbol | H |
| Atomic mass | 1.008 u |
| Density | 0.00008988 g/cm³ |
| Melting point | -259.34 °C (13.81 K) |
| Boiling point | -252.87 °C (20.28 K) |
| Electronegativity (Pauling) | 2.2 |
| Electron configuration | 1s1 |
| Atomic radius (van der Waals) | 120 pm |
| Oxidation states | +1, -1 |
| Physical state at 25 °C | gas |
| Family | nonmetal |
| Group and period | 1 / 1 |
| Discoverer and year | Henry Cavendish (1766) |
The discovery record belongs to Henry Cavendish, in 1766.
Neighbours on the table
Horizontally, one more lands on Helium (Z=2). Vertically, group 1 gathers relatives with similar behaviour: Lithium, Sodium, Potassium, Rubidium.
The story behind the name
The name comes from the Greek hydro and genes, water maker, coined by Lavoisier after burning the gas produced exactly that: water. Henry Cavendish, who isolated it in 1766, called it inflammable air and was so shy he communicated with his own servants through written notes. Roughly 90% of all atoms in the universe are hydrogen: nearly everything else is hydrogen recycled inside stars.
Physical and chemical data: PubChem Periodic Table (NCBI, compiling NIST and IUPAC), public domain, snapshot of 2026-07-10. Temperatures converted from kelvin; historical notes cross checked against classic chemistry references.
Last updated: · Methodology and sources