Strontium
[Kr] 5s² · 2 · 8 · 18 · 8 · 2
An alkaline earth metal that gives fireworks their deep scarlet. Strontium is chemically close to calcium and so builds into bone — which is what makes radioactive strontium-90 one of the nastiest fission products.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 38
- Atomic mass
- 87.62 а.е.м.
- Electron configuration
- [Kr] 5s²
- Electrons per shell
- 2 · 8 · 18 · 8 · 2
- Block
- s-block
- Group
- Alkaline earth metals
- Period
- 5
- Electronegativity (Pauling)
- 0.95
- Electronegativity (Allen)
- 0.96
- Atomic radius
- 219 pm
- Covalent radius
- 195 pm
- Van der Waals radius
- 249 pm
- Ionisation energy 1
- 549.5 kJ/mol
- Ionisation energy 2
- 1 064.2 kJ/mol
- Ionisation energy 3
- 4 138 kJ/mol
- Electron affinity
- 5.03 kJ/mol
- Common oxidation states
- +2
- Oxidation states
- +1, +2
Physical properties
- State at 25 °C
- solid
- Density
- 2.64 g/cm³
- Melting point
- 1 050 K · 776.9 °C
- Boiling point
- 1 650 K · 1 376.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 7.43 kJ/mol
- Heat of vaporisation
- 141 kJ/mol
- Specific heat capacity
- 0.301 J/(g·K)
- Thermal conductivity
- 35.4 W/(m·K)
Mechanical properties
- Young's modulus
- 15.7 GPa
- Shear modulus
- 6.03 GPa
- Bulk modulus
- no data
- Poisson ratio
- 0.28
- Mohs hardness
- 1.5
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 132 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- a = 608.49 pm
Abundance
- In the crust
- 370 mg/kg
- In the ocean
- 7.9 mg/L
- In the universe
- 40 mg/kg
- In the human body
- 4.6 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 84Sr | 0.56 % | stable | — |
| 86Sr | 9.86 % | stable | — |
| 87Sr | 7 % | stable | — |
| 88Sr | 82.58 % | stable | — |
| 90Sr | — | 28.9 yr | β− |
The strontium-87 to strontium-86 ratio in tooth enamel records the geology of where a person grew up, and archaeologists use it to reconstruct migrations.
Discovery
- Year of discovery
- 1790
- Discovered by
- Adair Crawford
- Where
- Scotland
- Origin of the name
- after Strontian, the Scottish village where strontianite was found
History
Adair Crawford noticed in 1790 that a mineral from the Scottish village of Strontian differed from known barium compounds. Davy isolated the metal in 1808.
Where it occurs
370 mg/kg of the crust. The main minerals are celestine and strontianite; the largest producers are Spain, China and Mexico.
How it is produced
From celestine via the carbonate, then aluminothermic reduction of the oxide. Little metal is made; demand is mostly for the salts.
Role in living things
Not considered essential, but it substitutes for calcium in bone. Strontium ranelate was used against osteoporosis until cardiovascular risks emerged.
Safety
Stable strontium is of low toxicity. Strontium-90 from fallout accumulates in bone and causes leukaemia and osteosarcoma — it was the central argument for banning atmospheric nuclear tests.
Uses
- Pyrotechnics: strontium nitrate gives the only genuinely red flame
- Ferrite magnets based on strontium hexaferrite
- Strontium-90 in thermoelectric generators and brachytherapy
- Additives in toothpaste for sensitive teeth
Curiosities
- Strontium is the only element named after a village.
- Only strontium produces the scarlet of fireworks; no other element gives that hue.
- Strontium isotopes in teeth reveal where someone spent their childhood.
- Strontium-90 drove the 1963 Partial Test Ban Treaty: it was turning up in children's milk teeth worldwide.