ElementsWhat is hydrogen?
Hydrogen is the lightest element and the most common one in the universe. Stars, including the Sun, are mostly hydrogen. On Earth almost all of it is locked in water and in living things. As a gas it has no colour or smell and burns very easily.
What is hydrogen used for?
Making ammonia for fertiliser, refining petrol and diesel, rocket fuel, and fuel cells that make electricity with only water as waste.
Where the name comes from
From the Greek words hydro and genes, meaning 'water former', because it makes water when it burns.
Key facts
- Symbol
- H
- Atomic number
- 1
- Atomic mass
- 1.0080 u
- Family
- Nonmetal
- Period
- 1
- Group
- 1
- Block
- s
- State at room temperature
- Gas
- Melting point
- -259.3 °C (13.81 K, -435 °F)
- Boiling point
- -252.9 °C (20.28 K, -423 °F)
- Density
- 0.00008988 g/cm³ (as a gas at 0 °C)
- Electrons per shell
- 1
- Electron configuration
- 1s1
- Common oxidation states
- +1, -1
- Electronegativity (Pauling)
- 2.2
- First ionisation energy
- 13.598 eV
- Electron affinity
- 0.754 eV
- Atomic radius (van der Waals)
- 120 pm
- Discovered
- 1766
Place in the periodic table
Hydrogen is element number 1. It sits in period 1 (row 1) of the periodic table, in group 1 (column 1), and belongs to the s-block. It is the first element. Just after it comes helium (2). In the same column, lithium is below it. Elements in one column tend to behave alike.
Family: Nonmetals.
Physical properties
At room temperature hydrogen is a gas. It melts at -259.3 °C and boils at -252.9 °C, so it stays liquid over a range of 6 degrees. One litre of the gas weighs about 0.09 grams at 0 °C and normal pressure. That is lighter than air, which weighs about 1.29 grams a litre. It has the 2nd lowest melting point of all elements.
Inside the atom
An atom of hydrogen has 1 protons in its nucleus and, when neutral, 1 electrons around it. The electrons are arranged in 1 shell: 1. The outermost shell holds 1 electron. Written in full, the electron configuration is 1s1.
Its electronegativity on the Pauling scale is 2.2. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 13.598 electronvolts (about 1,312 kilojoules per mole). One mole of hydrogen weighs 1.0080 grams, so a single gram contains about 5.97 × 1023 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains hydrogen with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.