Hydrogen (H)
Reactive nonmetal
Hydrogen is the lightest and most abundant element in the universe — roughly three quarters of all normal matter is hydrogen. On Earth it is almost always found combined with other elements, most famously with oxygen in water.
Position on the periodic table
Atomic properties
| Atomic number | 1 |
|---|---|
| Atomic mass | 1.008 amu |
| Electron configuration | 1s1 |
| Noble gas shorthand | 1s1 |
| Electrons per shell | 1 |
| Valence electrons (outer shell) | 1 |
| Common oxidation states | +1, -1 |
| Electronegativity (Pauling) | 2.2 |
| Covalent radius (approx.) | 31 pm |
| First ionization energy | 1312 kJ/mol |
| Electron affinity | 72.8 kJ/mol |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Density | 0.0899 g/L |
| Melting point | -259.16 °C (13.99 K) |
| Boiling point | -252.88 °C (20.27 K) |
| Appearance | colorless gas |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of hydrogen
Hydrogen's ground-state electron configuration is 1s1, usually shortened to 1s1. Its electrons occupy 1 shell (1), placing it in period 1 of the s-block. The 1 outer-shell electron drives its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of hydrogen
- Making ammonia for fertilisers (Haber process)
- Refining fuels and processing food oils
- Fuel cells and rocket propellant
- A promising clean energy carrier
Biological role: Essential to all life — part of water, carbohydrates, proteins, fats and DNA.
Occurrence: The most abundant element in the universe; on Earth mostly locked up in water and organic matter.
Common compounds of hydrogen
History and discovery
Discovered: 1766 — Henry Cavendish. Name origin: From Greek hydro (water) + genes (forming) — “water former”.
Henry Cavendish identified hydrogen as a distinct “inflammable air” in 1766, and Antoine Lavoisier later named it after discovering that burning it produces water.
Safety notes
Hydrogen gas is extremely flammable. Students should only ever see it handled in controlled classroom demonstrations.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Hydrogen
1. What is the chemical symbol of Hydrogen?
2. What is the atomic number of Hydrogen?
3. Which category does Hydrogen belong to?
4. What is the state of Hydrogen at room temperature?
5. Which period of the periodic table is Hydrogen in?
Hydrogen FAQs
How many protons does hydrogen have?
One. Hydrogen's atomic number is 1, so every hydrogen atom has exactly one proton — and, when neutral, one electron.
How many neutrons are in hydrogen?
Its most common isotope, protium (¹H), has zero neutrons — just one proton. The heavier isotopes deuterium (²H) and tritium (³H) have one and two neutrons.
Is hydrogen flammable?
Yes — hydrogen gas is highly flammable and forms explosive mixtures with air or oxygen. It is only ever handled in controlled conditions.
What is hydrogen used for?
Mostly to make ammonia for fertiliser (the Haber process) and to refine fuels. It is also used in fuel cells, to hydrogenate oils, and as a protective atmosphere in manufacturing.
Who discovered hydrogen?
Henry Cavendish, in 1766, who collected the gas released when metals reacted with acid and showed it was distinct from other gases. Antoine Lavoisier later named it.
How is hydrogen made?
Industrially, most hydrogen comes from steam reforming of natural gas; it is also produced by electrolysis, splitting water into hydrogen and oxygen with an electric current.
What is the atomic number of hydrogen?
Hydrogen's atomic number is 1 — every hydrogen atom has 1 protons in its nucleus.
What is the symbol for hydrogen?
H. From Greek hydro (water) + genes (forming) — “water former”.
Is hydrogen a metal, nonmetal, or metalloid?
Hydrogen is classified as a reactive nonmetal.
What state is hydrogen at room temperature?
At about 25 °C, hydrogen is a gas. It melts at -259.16 °C.
How many valence electrons does hydrogen have?
Hydrogen has 1 electron in its outer shell (shell pattern: 1).
Sources & references
- Hydrogen — Element information — Royal Society of Chemistry
Atomic masses and element data follow current IUPAC/NIST standard values. Educational content only — for graded or laboratory work, verify against your course materials. Last reviewed July 11, 2026.
Related elements
Keep working with this element
Spotted an error? Report a correction · Data sources