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Radium (Ra)

Radium (symbol Ra) is the chemical element with atomic number 88: an alkaline earth metal, solid at 0 °C, radioactive, with an atomic mass of 226 u. Discovered in 1898 (Pierre and Marie Curie).

Radium is an alkaline earth metal, a cousin of calcium and barium, discovered in 1898 by Pierre and Marie Curie. Gram for gram, it is more than a million times more radioactive than uranium, giving off enough energy to make some substances glow faintly in the dark. Hailed in the early 20th century as a miracle cure, it turned out to be fiercely dangerous. It is still used in medicine today, in a tightly controlled form.

Key facts

Atomic number

88

Symbol

Ra

French name

Radium

Atomic mass

226 u

Molar mass

[226] g/mol

Family

Alkaline earth metals

Position

period 7, group 2, s-block

State at 0 °C

Solid

Melting point

699.9 °C

Boiling point

1,736.9 °C

Density

5.5 g/cm³

Electronegativity (Pauling)

0.9

First ionization energy

509 kJ/mol

Atomic radius

215 pm

Electron configuration

[Rn] 7s²

Abundance in Earth's crust

0.000001 ppm (85th most abundant element)

Radioactive

yes

Discovery

1898, Pierre and Marie Curie

Origin of the name

From the Latin radius, ray.

What does radium look like?

A silvery-white metal, shiny when freshly prepared, that quickly blackens in air as a nitride layer forms. Its salts give off a bluish glow in the dark, and the metal is warm to the touch from its own radioactivity.

Where is radium found?

It forms continuously in uranium ores through the decay of uranium-238, but in extremely dilute form: barely a third of a gram of radium per tonne of uranium. Traces also occur in some spring waters and in soil, from which its decay product, radon gas, escapes.

Natural sources

• Uraninite (pitchblende)
• Carnotite
• Autunite

How is radium produced?

Historically, it was extracted from tonnes of uranium ore residues through grueling rounds of repeated crystallization. Radium-226 is hardly produced anymore. The radium-223 used in medicine comes from generators containing actinium-227, itself produced in nuclear reactors.

Top producers

• Norway (medical radium-223)

What is radium used for?

• Treatment of bone metastases from prostate cancer (radium-223)
• Formerly: luminous paint for watch dials and instruments
• Formerly: cancer radiotherapy (brachytherapy)
• Historical: the “curie” unit was defined from one gram of radium

In everyday life

• Old glow-in-the-dark watches and alarm clocks from before 1960 (still radioactive)
• Vintage cockpit instruments from military aircraft
• Some hospital nuclear medicine departments

Role in living things

No useful role. The body mistakes it for calcium and locks it into bone, where it irradiates the bone marrow for years. That very affinity for bone is what medicine exploits to target bone metastases.

Hazards of radium

Highly radiotoxic if swallowed or inhaled: anemia, bone necrosis, bone cancer. As it decays it produces radon, a radioactive gas that builds up in closed rooms. Old radium items should be handled with care and never opened.

Cosmic origin

• None of it survives from the formation of the Solar System: it is constantly being created by the radioactive decay of uranium and thorium.

History of radium

In 1898, Pierre and Marie Curie, helped by Gustave Bémont, noticed that pitchblende was more radioactive than its uranium alone could explain. After years of work in a Paris shed, they isolated a tenth of a gram of radium chloride in 1902. Marie Curie and André Debierne obtained the pure metal in 1910, earning Marie her second Nobel Prize in 1911.

Did you know?

• In the 1920s, the “Radium Girls,” American factory workers who shaped their brushes to a point with their lips while painting dials, developed cancers of the jaw; their lawsuit helped advance labor law.
• Radium creams, waters, chocolate and even suppositories were sold before its dangers were recognized.
• Marie Curie's lab notebooks are still radioactive: they are kept in lead-lined boxes at the National Library of France.
• Its name comes from the Latin radius, “ray.”

Isotopes of radium

No stable isotopes; all of them are radioactive. Radium-226, discovered by Marie and Pierre Curie, occurs in traces in uranium ores.

• radium-223: radioactive, half-life 11.4 days. The drug Xofigo, which targets bone metastases from prostate cancer.
• radium-224: radioactive, half-life 3.63 days
• radium-225: radioactive, half-life 14.9 days. Used to produce the actinium-225 used in medicine.
• radium-226: radioactive, half-life 1,600 years. The Curies' radium, once used in radiotherapy and in the luminous paint on watch dials.
• radium-228: radioactive, half-life 5.75 years

Related elements

Same family (alkaline earth metals): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba).

Same column (group 2): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba).