Radium
Atomic Data
| Atomic Number | 88 |
| Symbol | Ra |
| Atomic Weight | 226 u |
| Density (STP) | 5.5 g/cm³ |
| Melting Point | 699.85 °C (973 K) |
| Boiling Point | 1736.85 °C (2010 K) |
| Electronegativity | 0.9 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s2 |
| Oxidation States | +2 |
| Phase at STP | Solid |
| Category | Alkaline-Earth Metal |
| Period / Group | 7 / 2 |
| CAS Number | 7440-14-4 |
Electron Configuration
[Rn] 7s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 2 | 80 |
| P | 6 | 6p | 6 | 86 |
| Q | 7 | 7s | 2 | 88 |
| Total | 88 | 88 | ||
Isotopes of Radium
Radium has two naturally occurring stable isotopes. The most abundant is ²²⁶Ra, comprising None% of all naturally occurring Radium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Radium-226 | ²²⁶Ra | 88 | 138 | trace | Stable |
| Radium-228 | ²²⁸Ra | 88 | 140 | trace | Stable |
Abundance & Occurrence
Radium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Radiation: alpha, beta, and gamma: Radium-226 (t½ = 1600 years) and its decay products emit alpha, beta, and gamma radiation; ingested or inhaled radium accumulates in bone (mimicking calcium) and causes bone cancer and leukaemia.
- Radium dial painters: historical lesson: The Radium Girls case established that chronic low-dose radium ingestion (from lip-pointing brushes) causes osteosarcoma; this led to foundational occupational radiation protection regulations.
- Radon generation: Radium decay produces radon-222 gas; radium-containing materials in unventilated spaces accumulate radon, compounding the radiation hazard.
- Contamination control: Any radium work requires stringent surface contamination monitoring; radium-contaminated sites and legacy equipment (luminous instruments, antique medical devices) require specialist radiological survey and decontamination before reuse or disposal.
Radium in the Real World
Real-World Uses
- Cancer brachytherapy (historical): Radium-226 sealed in gold or platinum needles and tubes was the first widely used radiotherapy source for cancer treatment after Marie Curie's discovery; it was standard clinical practice from the 1910s to the 1970s before being replaced by safer cobalt-60, iridium-192, and caesium-137 sources.
- Luminous paint (historical): Radium mixed with zinc sulfide phosphor was painted on instrument dials, watches, and aircraft instruments to make them glow in the dark; the serious health consequences for dial painters (radium jaw, bone cancers) led to the prohibition of radium luminous paint in most countries by the 1970s.
- Neutron source (Ra-Be): Radium-beryllium (Ra-Be) sources produce neutrons via (alpha,n) reactions on beryllium; they were widely used in early nuclear physics research, oil well logging, and neutron radiography before being replaced by californium-252 and accelerator sources.
- Uranium-radium geological dating: The uranium-238 to radium-226 secular equilibrium ratio in minerals is used in geological dating and in tracing ocean circulation and carbonate formation in palaeoceanography and geochemistry.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is radium used for?
Radium is used mainly in cancer treatment: radium-223 dichloride (Xofigo) is an approved drug that targets bone metastases from prostate cancer, delivering alpha radiation to tumour sites. Historically, radium was used extensively in luminous watch and instrument dials (mixed with zinc sulphide), which caused radiation poisoning among the 'Radium Girls' who painted them. Most historical industrial and medical uses of radium have been replaced by safer alternatives.
Is radium dangerous?
Yes, radium is highly radioactive and toxic. Because radium is chemically similar to calcium, it is incorporated into bones if ingested, where its radiation causes bone cancer, leukaemia, and other cancers over years to decades. The Radium Girls: young women who painted luminous dials in the 1910s–1920s and were told to point their brushes with their lips: suffered horrific radiation injuries, including jaw necrosis and cancer, in a landmark occupational health scandal.
How was radium discovered?
Radium was discovered in December 1898 by Marie and Pierre Curie while processing pitchblende uranium ore. After noticing the ore was far more radioactive than could be explained by uranium alone, they laboriously processed tonnes of ore to isolate tiny amounts of new elements. Radium was isolated as a chloride salt. Marie Curie received the Nobel Prize in Chemistry in 1911 specifically for the discovery and isolation of radium and polonium.
What is the Radium Girls story?
The Radium Girls were young female factory workers at the United States Radium Corporation and similar factories in the 1910s–1920s who painted watch and instrument dials with radium-based luminous paint. Supervisors told them the radium was harmless and encouraged them to lip-point their brushes to get fine tips. Over subsequent years, many developed radiation-induced cancers: particularly jaw bone necrosis (radium necrosis) and bone cancer. Their legal battles against the company in the late 1920s established crucial precedents for occupational health regulation and workers' rights to sue employers for work-related illness.