Radium (Ra)

The Radium Girls — young women who painted luminous watch dials in New Jersey and Illinois in the 1910s and 1920s, and were taught to point the brushes with their lips — developed jaw necrosis and bone cancers, and the lawsuits that followed established an employee's right to sue over occupational disease. Radium behaves chemically like calcium, so the body files it into bone and it stays there. Marie Curie processed several tonnes of pitchblende by hand to isolate about a tenth of a gram of radium chloride; her notebooks are still radioactive and are kept in lead-lined boxes.

Properties

Atomic number

88

Symbol

Ra

Mass number of most stable isotope

[226]

Category

Alkaline earth metal

Group

2

Period

7

Block

s-block

Electron configuration

[Rn] 7s²

Electrons per shell

2, 8, 18, 32, 18, 8, 2

Melting point

973 K — 699.9 °C — 1291.7 °F

Boiling point

1,413 K — 1139.8 °C — 2083.7 °F

Density

5.5 g/cm³

Electronegativity

0.9 (Pauling)

Oxidation states

+2

Discovered

1898 by Marie and Pierre Curie

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s²

Noble gas shorthand

[Rn] 7s²

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 18 · P: 8 · Q: 2

What it is used for

• Radium-223 for treating bone metastases from prostate cancer
• Historically, luminous paint on watch and instrument dials
• Historically, brachytherapy needles for cancer treatment

Hazards

• Bone-seeking alpha emitter with a 1,600-year half-life
• Decays to radon gas, so a sealed radium source pressurises and can leak
• Historic radium dials, clocks and quack medical devices remain hazardous today

No stable isotope; the mass given is the mass number of radium-226, the longest-lived at 1,600 years. Sources disagree on the bulk constants: the boiling point is variously given as 1,413 K and 2,010 K, and the density as 5 or 5.5 g/cm³. Both figures come from small samples that were, unavoidably, heating themselves.

Neighbours in the table

Group 2

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Radium sits in group 2 with beryllium, magnesium, calcium, strontium, barium.