Radium
[Rn] 7s² · 2 · 8 · 18 · 32 · 18 · 8 · 2
The element that early twentieth-century industry put into toothpaste, cosmetics and drinking water before anyone understood what it did to people. Radium glows in the dark by its own light and became the emblem of an era of naive enthusiasm for radioactivity.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 88
- Atomic mass
- 226 а.е.м. ≈
- Electron configuration
- [Rn] 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 8 · 2
- Block
- s-block
- Group
- Alkaline earth metals
- Period
- 7
- Electronegativity (Pauling)
- 0.9
- Electronegativity (Allen)
- 0.89
- Atomic radius
- 283 pm
- Covalent radius
- 221 pm
- Van der Waals radius
- 283 pm
- Ionisation energy 1
- 509.3 kJ/mol
- Ionisation energy 2
- 979 kJ/mol
- Electron affinity
- 9.6 kJ/mol
- Common oxidation states
- +2
- Oxidation states
- +2
Physical properties
- State at 25 °C
- solid
- Density
- 5.5 g/cm³
- Melting point
- 973 K · 699.9 °C
- Boiling point
- 2 010 K · 1 736.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 8.5 kJ/mol
- Heat of vaporisation
- 113 kJ/mol
- Specific heat capacity
- 0.094 J/(g·K)
- Thermal conductivity
- 18.6 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 1 000 nΩ·m
- Magnetic ordering
- non-magnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- body-centred cubic (bcc)
- Lattice constants
- a = 514.8 pm
Abundance
- In the crust
- 9·10⁻⁷ mg/kg
- In the ocean
- 8.9·10⁻¹⁰ mg/L
- In the universe
- no data
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 223Ra | — | 11.43 d | α |
| 226Ra | — | 1 600.28 yr | α |
| 228Ra | — | 5.74 yr | β− |
Radium-226, half-life 1600 years, is the main natural isotope. Radium-223 is used today in targeted alpha therapy of prostate cancer bone metastases.
Discovery
- Year of discovery
- 1898
- Discovered by
- Marie and Pierre Curie
- Where
- France
- Origin of the name
- from Latin radius (ray)
History
Marie and Pierre Curie isolated radium in 1898 after processing tonnes of pitchblende in an unventilated shed. It won Marie a second Nobel Prize, in chemistry, in 1911.
Where it occurs
About 10⁻⁶ mg/kg of the crust. It forms in the uranium series and occurs wherever uranium does.
How it is produced
Extracted from uranium ores; production essentially ceased once artificial isotopes became available.
Role in living things
No biological role. Radium is chemically like calcium and builds into bone, where it irradiates the marrow.
Safety
The Radium Girls — workers who painted luminous dials and pointed their brushes with their lips — died in numbers from osteosarcoma and jaw necrosis. Their 1928 lawsuit laid the foundations of occupational disease law.
Uses
- Luminous paint for dials and watches (banned)
- Brachytherapy in the first half of the twentieth century (displaced by other isotopes)
- A radon source for the medical procedures of that era
Curiosities
- The Radium Girls' case changed occupational disease law in the United States.
- Radium glows pale blue: that is the air it ionises, not the metal itself.
- Marie Curie's notebooks are still radioactive and are kept in lead-lined boxes.
- Radium-223 returned to medicine a century later, this time as a precise targeted drug.