Radium (Ra)
Alkaline earth metal · Radioactive
Radium made the Curies famous and radioactivity a household word. Its salts glow with eerie blue light and were once painted on watch dials — until the tragic fate of the “Radium Girls” dial painters exposed the danger.
Position on the periodic table
Atomic properties
| Atomic number | 88 |
|---|---|
| Atomic mass | 226 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 |
| Noble gas shorthand | [Rn] 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +2 |
| Electronegativity (Pauling) | 0.9 |
| Covalent radius (approx.) | 221 pm |
| First ionization energy | 509.3 kJ/mol |
| Electron affinity | 9.6 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 5.5 g/cm³ |
| Melting point | 959.85 °C (1233 K) |
| Boiling point | 1736.8 °C (2010 K) |
| Appearance | silvery white metallic |
| Radioactive | Yes |
| Origin | Occurs naturally |
Electron configuration of radium
Radium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2, usually shortened to [Rn] 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 18, 8, 2), placing it in period 7 of the s-block. The 2 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of radium
- Historic luminous paint (banned)
- Historic cancer therapy, now replaced by safer isotopes
- Ra-223 for targeted bone-cancer treatment
Biological role: None — it substitutes for calcium in bone, with dire results.
Occurrence: Trace constituent of uranium ores — tonnes of ore yield milligrams of radium.
Common compounds of radium
RaCl2
Radium chloride
History and discovery
Discovered: 1898 — Pierre Curie. Name origin: From Latin radius, “ray”.
Marie and Pierre Curie isolated radium from tonnes of pitchblende in 1898, earning Marie her second Nobel Prize in 1911.
Safety notes
Severely radiotoxic; historic radium dials and products should be treated as radioactive waste.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Radium
1. What is the chemical symbol of Radium?
2. What is the atomic number of Radium?
3. Which category does Radium belong to?
4. What is the state of Radium at room temperature?
5. Which period of the periodic table is Radium in?
Radium FAQs
What is the atomic number of radium?
Radium's atomic number is 88 — every radium atom has 88 protons in its nucleus.
What is the symbol for radium?
Ra. From Latin radius, “ray”.
Is radium a metal, nonmetal, or metalloid?
Radium is classified as a alkaline earth metal.
What state is radium at room temperature?
At about 25 °C, radium is a solid. It melts at 959.85 °C.
How many valence electrons does radium have?
Radium has 2 electrons in its outer shell (shell pattern: 2, 8, 18, 32, 18, 8, 2).
What is radium used for?
Key uses include: historic luminous paint (banned); historic cancer therapy, now replaced by safer isotopes; ra-223 for targeted bone-cancer treatment.
Related elements
Keep working with this element
Spotted an error? Report a correction · Data sources