Radium Element Facts

The chemical element radium is classed as an alkali earth metal. It was discovered in 1898 by Marie S. Curie and her husband Pierre.

World War II aircraft gauges containing radium.

World War II aircraft gauges containing radium. The radium glows allowing the gauges to be read in darkness. Image Ref.(1)


Data Zone

Classification: Radium is an alkali earth metal
Color: silvery white
Atomic weight: (226), no stable isotopes
State: solid
Melting point: 700 oC, 973 K
Boiling point: 1500 oC, 1773 K
Electrons: 88
Protons: 88
Neutrons in most abundant isotope: 138
Electron shells: 2,8,18,32,18,8,2
Electron configuration: [Rn] 7s2
Density @ 20oC: 5.5 g/cm3
Atomic volume: 45.20 cm3/mol
Structure: bcc: body-centered cubic
Specific heat capacity 0.12 J g-1 K-1
Heat of fusion 8.5 kJ mol-1
Heat of atomization 159 kJ mol-1
Heat of vaporization 113 kJ mol-1
1st ionization energy 509.4 kJ mol-1
2nd ionization energy 979.1 kJ mol-1
3rd ionization energy
Electron affinity
Minimum oxidation number 0
Min. common oxidation no. 0
Maximum oxidation number 2
Max. common oxidation no. 2
Electronegativity (Pauling Scale) 0.9
Polarizability volume 38.3 Å3
Reaction with air vigorous, ⇒ RaO2, Ra3N2
Reaction with 15 M HNO3
Reaction with 6 M HCl
Reaction with 6 M NaOH
Oxide(s) RaO
Chloride(s) RaCl2
Atomic radius 215 pm
Ionic radius (1+ ion)
Ionic radius (2+ ion) 162 pm
Ionic radius (3+ ion)
Ionic radius (1- ion)
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity 18.6 W m-1 K-1
Electrical conductivity 1 x 106 S m-1
Freezing/Melting point: 700 oC, 973 K

Discovery of Radium

Radium was discovered in 1898 in Paris, by Marie S. Curie and her husband Pierre in pitchblende (mainly uranium dioxide, UO2).

If pitchblende contains 50 percent uranium oxides, about eight tons of it is needed to extract 1 gram of radium.

Already that year the Curies had discovered polonium, a radioactive element whose properties they said were similar to bismuth’s.

Now, in radium – in the form of radium bromide – they had discovered a further radioactive element whose chemistry was very similar to that of group II metal barium.

Metallic radium was first isolated in 1910 by Marie Curie and Andre Debierne by the electrolysis of a solution of pure radium chloride.

The element’s name comes from the Latin word ‘radius’ meaning ray, after the rays emitted by this radioactive element.

In the discovery of radioactivity, chemists realized that one of alchemy’s dreams – the transmutation of elements – was possible.

People were sold radium to drink for the good of their health! It would also cure insanity!

Appearance and Characteristics

Harmful effects:

Radium is highly radioactive and hence carcinogenic. Microscopic quantities of radium in the environment can lead to some accumulation of radium in bone tissue. Radium, like calcium, is a group II element and our bodies treat it in a similar way.


Radium is a silvery-white metal. It is highly radioactive and its decay product, radon gas, is also radioactive. One result of radium’s intense radioactivity is that the metal and its compounds glow in the dark.

When it is exposed to air, it reacts with nitrogen to quickly form a black coating of radium nitride.

Radium’s chemistry is similar to that of the other alkali earth metals. It reacts very vigorously with water to form hydrogen gas and radium hydroxide. It reacts with even more vigorously with hydrochloric acid to form radium chloride.

Uses of Radium

Radium was used in the production of luminous paints, but this is now considered too dangerous.

Radium chloride was used medicinally to produce radon gas for cancer treatment. Safer treatments are now available.

Abundance and Isotopes

Abundance earth’s crust: 1 part per trillion by weight, 0.1 parts per trillion by moles

Abundance solar system: parts per billion by weight, part per billion by moles

Cost, pure: $ per 100g

Cost, bulk: $ per 100g

Source: Radium is present in tiny amounts in all uranium ores – it arises from uranium decay. Radium is present at very low concentrations in sea water. Most radium, 226Ra, arises from the decay of the plentiful 238U, hence radium is obtained in residues taken from uranium production.

Isotopes: Radium has 33 isotopes whose half-lives are known, with mass numbers 202 to 234. None is stable. 226Ra has the longest half-life of 1602 years.


1. Photo: EPA

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