Hydrogen
Element 1 · Nonmetal
Hydrogen is the simplest and lightest of all elements, with a single proton and a single electron. On Earth it rarely travels alone; it pairs up as H2 gas or locks into compounds such as water and hydrocarbons. It was the first element to form after the Big Bang, and it still powers the Sun, where fusion turns hydrogen into helium and releases starlight. Chemists value hydrogen because it reacts with almost everything: it burns in oxygen to make water, teams up with nitrogen to make ammonia fertilizer, and sits at the heart of every acid. Life itself runs on hydrogen — it shuttles energy in cells and holds proteins and DNA in shape through hydrogen bonding.
Key facts
| Atomic number | 1 |
|---|---|
| Atomic weight | 1.008 |
| Category | Nonmetal |
| Group / Period | 1 / 1 |
| Block | s |
| Electron configuration | 1s1 |
| Common oxidation states | +1, -1 |
| State at STP | Gas |
| Electronegativity | 2.20 |
| Atomic radius | 53 pm |
| Density | 0.00009 g/cm³ |
| Melting point | -259.16 °C |
| Boiling point | -252.87 °C |
Occurrence
About 75 percent of all ordinary matter in the universe is hydrogen, concentrated in stars and gas clouds. On Earth, free H2 is scarce because it escapes to space; nearly all hydrogen here is bound into water, natural gas, petroleum, and living things. Traces of hydrogen gas seep from some rocks and volcanoes.
Applications
Ammonia and fertilizer production
Petroleum refining and clean-fuel processing
Hydrogenation of vegetable oils
Rocket propellant with liquid oxygen
Fuel cells and emerging clean energy
Methanol and chemical manufacturing
Common compounds
- Water (H2O)
- Ammonia (NH3)
- Methane (CH4)
- Hydrochloric acid (HCl)
- Hydrogen peroxide (H2O2)
- Glucose (C6H12O6)
Hydrogen is about 14 times lighter than air, which is why it lifts balloons so eagerly. Never try this near flame, though — H2 burns explosively.
Data source: IUPAC standard atomic weights 2021