ElementsWhat is radium?
Radium is a silvery-white radioactive metal discovered by Marie and Pierre Curie. It glows faintly in the dark.
What is radium used for?
Once used in glowing watch dials, which harmed the workers who painted them. Today a radioactive form is used in some cancer treatment.
Where the name comes from
From the Latin word radius, ray.
Key facts
- Symbol
- Ra
- Atomic number
- 88
- Atomic mass
- 226.02541 u
- Family
- Alkaline earth metal
- Period
- 7
- Group
- 2
- Block
- s
- State at room temperature
- Solid
- Melting point
- 699.9 °C (973 K, 1,292 °F)
- Boiling point
- 1,140 °C (1,413 K, 2,084 °F)
- Density
- 5 g/cm³
- Electrons per shell
- 2, 8, 18, 32, 18, 8, 2
- Electron configuration
- [Rn]7s2
- Common oxidation states
- +2
- Electronegativity (Pauling)
- 0.9
- First ionisation energy
- 5.279 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 283 pm
- Discovered
- 1898
Place in the periodic table
Radium is element number 88. It sits in period 7 (row 7) of the periodic table, in group 2 (column 2), and belongs to the s-block. Just before it comes francium (87), and just after it comes actinium (89). In the same column, barium is above it. Elements in one column tend to behave alike.
Family: Alkaline earth metals.
Physical properties
At room temperature radium is a solid. It melts at 699.9 °C and boils at 1,140 °C, so it stays liquid over a range of 440 degrees. Its density is 5 grams per cubic centimetre, so a one-litre block would weigh about 5 kilograms. By density it ranks 63rd among the 96 elements with a measured value.
Inside the atom
An atom of radium has 88 protons in its nucleus and, when neutral, 88 electrons around it. The electrons are arranged in 7 shells: 2, 8, 18, 32, 18, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Rn]7s2.
Its electronegativity on the Pauling scale is 0.9. 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 5.279 electronvolts (about 509 kilojoules per mole). One mole of radium weighs 226.02541 grams, so a single gram contains about 2.66 × 1021 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 radium 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.