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It's Elemental

The Element Radium

[Click for Isotope Data]


88 Ra Radium 226

Atomic Number: 88

Atomic Weight: 226

Melting Point: 973 K (700°C or 1292°F)

Boiling Point: 1413 K (1140°C or 2084°F)

Density: 5 grams per cubic centimeter

Phase at Room Temperature: Solid

Element Classification: Metal

Period Number: 7

Group Number: 2

Group Name: Alkaline Earth Metal

Special Notes: Radioactive

What's in a name? From the Latin word for ray, radius.

Say what? Radium is pronounced as RAY-dee-em.

History and Uses:

Radium was discovered by Marie Sklodowska Curie, a Polish chemist, and Pierre Curie, a French chemist, in 1898. Marie Curie obtained radium from pitchblende, a material that contains uranium, after noticing that unrefined pitchblende was more radioactive than the uranium that was separated from it. She reasoned that pitchblende must contain at least one other radioactive element. Curie needed to refine several tons of pitchblende in order to obtain tiny amounts of radium and polonium, another radioactive element discovered by Curie. One ton of uranium ore contains only about 0.14 grams of radium. Today, radium can be obtained as a byproduct of refining uranium and is usually sold as radium chloride (RaCl2) or radium bromide (RaBr2) and not as a pure material.

Radium's most stable isotope, radium-226, has a half-life of about 1600 years. It decays into radon-222 through alpha decay or into lead-212 by ejecting a carbon-14 nucleus.

The Curie, a unit used to describe the activity of a radioactive substance, is based on radium-226. It is equal to the number of atoms in a one gram sample of radium-226 that will decay in one second, or 37,000,000,000 decays per second.

Radium had been used to make self-luminous paints for watches, aircraft instrument dials and other instrumentation, but has largely been replaced by cobalt-60, a less dangerous radioactive source. A mixture of radium and beryllium will emit neutrons and is used as a neutron source. Radium is used to produce radon, a radioactive gas used to treat some types of cancer. A single gram of radium-226 will produce 0.000l milliliters of radon a day.

Radium is about one million times more active than uranium. The lab notebooks used by the Curies are too highly contaminated to be safely handled today.

Estimated Crustal Abundance: 9×10-7 milligrams per kilogram

Estimated Oceanic Abundance: 8.9×10-11 milligrams per liter

Number of Stable Isotopes: 0 (View all isotope data)

Ionization Energy: 5.279 eV

Oxidation States: +2

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10   4f14

5s2   5p6   5d10

6s2   6p6


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For questions about this page, please contact Steve Gagnon.