Radium Facts

Radium Chemical & Physical Properties

Radium is a bright silver radioactive metal that darkens upon exposure to air.
Radium is a bright silver radioactive metal that darkens upon exposure to air. This photo shows radium that has been electroplated onto copper foil and then coated with polyurethane to keep it from reacting with air. grenadier, Creative Commons License

Radium Basic Facts

Atomic Number: 88

Symbol: Ra

Atomic Weight: 226.0254

Discovery: Discovered by Pierre and Marie Curie in 1898 (France/Poland). Isolated in 1911 by Mme. Curie and Debierne.

Word Origin: Latin radius: ray

Isotopes: Sixteen isotopes of radium are known. The most common isotope is Ra-226, which has a half-life of 1620 years.

Properties: Radium is an alkaline earth metal. Radium has a melting point of 700°C, boiling point of 1140°C, specific gravity estimated to be 5, and valence of 2. Pure radium metal is bright white when freshly prepared, although it blackens upon exposure to air. The element decomposes in water. It is somewhat more volatile than the element barium. Radium and its salts exhibit luminescence and impart a carmine color to flame. Radium emits alpha, beta, and gamma rays. It produces neutrons when mixed with beryllium. A single gram of Ra-226 decays at the rate of 3.7x1010 disintegrations per second. [The curie (Ci) is defined to be the quantity of radioactivity which has the same rate of disintegration as 1 gram of Ra-226.] A gram of radium produces around 0.0001 ml (STP) of radon gas (emanation) per day and about 1000 calories per year. Radium loses about 1% of its activity over 25 years, with lead as its final disintegration product. Radium is a radiological hazard. Stored radium requires ventilation to prevent the build-up of radon gas.

Uses: Radium has been used to produce neutron sources, luminous paints, and medical radioisotopes.

Sources: Radium was discovered in pitchblende or uraninite. Radium is found in all uranium minerals. There is approximately 1 gram of radium for each 7 tons of pitchblende. Radium was first isolated by electrolysis of a radium chloride solution, using a mercury cathode. The resulting amalgam yielded pure radium metal upon distillation in hydrogen. Radium is commercially obtained as its chloride or bromide and tends not to be purified as an element.

Element Classification: alkaline earth metal

Radium Physical Data

Density (g/cc): (5.5)

Melting Point (K): 973

Boiling Point (K): 1413

Appearance: silvery white, radioactive element

Atomic Volume (cc/mol): 45.0

Ionic Radius: 143 (+2e)

Specific Heat (@20°C J/g mol): 0.120

Fusion Heat (kJ/mol): (9.6)

Evaporation Heat (kJ/mol): (113)

Pauling Negativity Number: 0.9

First Ionizing Energy (kJ/mol): 509.0

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)


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