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Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.


Radium is a radioactive element in Group 2 (IIA) and Row 7 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Radium was discovered in 1898 by Marie Curie (1867-1934) and her husband, Pierre Curie (1867-1934). It was found in an ore of uranium called pitchblende. The alkaline earth metals also include beryllium, magnesium, calcium, strontium, and barium.

Radium is luminescent, meaning it gives off radiation that can be seen in the dark. Because of its radiation, however, it has relatively few uses.

Discovery and naming

The discovery of radium is one of the most interesting stories in science. The story has been told over and over again in books, articles, and motion pictures, and on television.




Group 2 (IIA)
Alkaline earth metal


The story begins with the research of French physicist Antoine-Henri Becquerel (1852-1908). In 1896, Becquerel made a discovery about the ore called pitchblende. Pitchblende contains the element uranium. Becquerel found that pitchblende gives off radiation that acts much like light. The main difference is that the radiation from pitchblende is not visible to the human eye.

Becquerel's discovery caused great excitement among scientists. Many physicists stopped their own research and began to study this new curiosity. One of those who did so was a graduate student named Marie Sklodowska Curie. Marie had been born in Warsaw, Poland, as Marya Sklodowska. In 1891, she moved to Paris, France, to study physics. Three years later she met another physicist, Pierre Curie. The two were married in 1895.

Marie and Pierre were especially interested in learning more about pitchblende. What was in the ore that was giving off radiation, they asked. To answer this question, they purified huge amounts of the natural ore. Eventually, they isolated a new element that gave off radiation much more intensely than did the pitchblende itself. The Curies named the new element polonium.

But they were not finished with their research. They thought at least one other element might be in the pitchblende. So they continued the process of purification. In 1898, they isolated a second new element. They called this element radium. They chose this name because the element gives off such intense radiation. It took the Curies another four years to prepare one gram of the element. To do so, they had to sift through more than seven metric tons of pitchblende!

Physical properties

Radium is a brilliant white metal with a melting point of 700°C (1,300°F) and a boiling point of 1,737°C (3,159°F). Its density is 5.5 grams per cubic centimeter.

What time is it?

R adium was once used in paint that was applied on the hands and numbers of clocks and watches. The visible radiation it emitted made it possible to read the numbers in the dark. But the radiation proved very harmful to people who applied the radium paint to a watch or clock.

The technique they used was to make a sharp point on their brushes by twirling the brush between their lips. They then dipped the brush into radioactive radium paint. The dipping and twirling sequence ultimately caused the painters to get a lot of radium on their lips. This resulted in many cases of lip and mouth cancer among those painters. So radium is no longer used on clocks and watches.

Chemical properties

Radium combines with most non-metals, including oxygen, fluorine, chlorine, and nitrogen. It also reacts with acids with the formation of hydrogen gas. Radium's chemical properties are of much less interest than its radioactivity, however.

Occurrence in nature

The amount of radium in the Earth's crust is very small. Its abundance has been estimated to be about 0.0000001 parts per million. It occurs not only in pitchblende, but in all ores that contain uranium. It is formed when uranium gives off radiation and breaks down.


Four naturally occurring isotopes of radium are known. They are radium-223, radium-224, radium-226, and radium-228. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Only radium-226 has any commercial applications. It has a half life of 1,620 years. After that period of time, only half of the original sample would remain. The half life of a radioactive element is the time it takes for half of a sample of the element to break down. The other three isotopes have half lives of only a few days or years. These short half lives make it difficult to work with the isotopes.

The only isotope now used very often, radium-226, is generally not used directly. Instead, it is used to make radon gas. Radon gas is one of the products formed when radium breaks down. The radon gas is easier and safer to work with than is the radium itself.


The process by which radium is obtained is similar to that used by the Curies. The metal is separated from other substances found in pitchblende by a long series of chemical reactions.

Uses and compounds

Because of its history, radium is a very interesting and important element. But radium and its compounds have relatively few uses. In fact, no more than about two kilograms (five pounds) of radium is made each year. The small amount of radium that is available is used for medical purposes. The radium is used to produce radon gas which, in turn, is used to treat cancer. Radiation given off by radium is sometimes used also to study the composition of metals, plastics, and other materials.

Health effects

Like all radioactive materials, radium is a dangerous substance to handle. The radiation it gives off can kill living cells. This property is desirable in treating cancer. Killing cancer cells can help a patient recover from the disease. But great care must be taken in using radium for this purpose. Its radiation can also kill healthy cells. People who work with radium must take great care that they do not get the element on their skin, swallow it, or inhale its fumes.

Marie Curie herself eventually died from working with radium. She developed leukemia and died in 1934.

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melting point: 700°C
boiling point: 1,140°C
density: 5.00 g/cm3
most common ions: Ra2+

Radium is the last of the alkaline earth metals comprising the second column of the Periodic Table. While there are twenty-five known isotopes of radium (only four of which are found naturally), all of them are radioactive. Of these isotopes, radium-226 is the most common, with a half-life of about 1,600 years.

Radium was first isolated in 1898 by Marie Sklodowska Curie and her husband, Pierre Curie. They were studying the radioactivity of pitchblende, a uranium-rich ore, and noticed that the ore was still radioactive with all the uranium removed. After years of painstaking work, the Curies eventually isolated radium and named it for the Latin word radius, meaning "ray." For this work, Madame Curie was awarded the Nobel Prize in Chemistry in 1911, her second such honor (the first one, in physics, shared with her husband and Henri Becquerel in 1903 for their initial studies of radioactivity).

Radium is rare in nature, being only the eighty-fifth most abundant element in Earth's crust. When the Curies and their assistant, Gustave Bemont, first isolated radium, they had to reduce many tons of pitchblende ore to obtain only a few grams of the element. As a metal, radium has a silvery white color and is luminous due to its inherent radioactivity. In the past, radium salts were mixed with phosphorescent zinc sulfide into a paint that was placed on the faces of some clocks and watches so that they could be seen at night. However, the workers who painted the clocks suffered and often died of radiation poisoning and cancer, and so the practice was ended. These days, the uses for radium are as rare as the element itself, with annual world production totaling less than 1 kilogram (2.2 pounds).

see also Curie, Marie Sklodowska.

David A. Dobberpuhl


Heiserman, David L. (1992). Exploring Chemical Elements and Their Compounds. Blue Ridge Summit, PA: Tab Books.

Krebs, Robert E. (1998). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Westport, CT: Greenwood Press.

Stwertka, Albert (2002). A Guide to the Elements, 2nd edition. New York: Oxford University Press.

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radium (symbol Ra) White, radioactive, metallic element of the alkaline-earth metals, first discovered (1898) in pitchblende by French physicists Pierre and Marie Curie; the metal is present in uranium ores. It is used in radiotherapy to treat tumours. Radium has 16 isotopes, which emit alpha, beta and gamma radiation, as well as heat. Radon gas is a decay product. Properties: at.no. 88; r.a.m. 226.025; r.d. 5.0; m.p. 700°C (1292°F); b.p. 1140°C (2084°F); most stable isotope Ra226 (half-life 1622 years).

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ra·di·um / ˈrādēəm/ • n. the chemical element of atomic number 88, a rare radioactive metal of the alkaline earth series. It was formerly used as a source of radiation for radiotherapy. (Symbol: Ra)

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radium (ray-diŭm) n. a radioactive metallic element that emits alpha and gamma rays during its decay into other elements. The gamma radiation was formerly employed in radiotherapy for the treatment of cancer. Symbol: Ra.

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radium XIX. f. L. radius RAY1; see -IUM.

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