| Strontium - Sr
CAS: 7440-24-6 Description: Soft, silvery yellow metal Classification: Alkaline Earth Date of Discovery: 1790 Discoverer: A. Crawford Name Origin: Strontian, town in Scotland |
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Atomic Number: 38
Number of Neutrons: 50 Atomic Mass: 87.62(1) amu Melting Point: 777 °C Boiling Point: 1382 °C Density (293 K): 2.54 g/cm3 Atomic volume: 33.7 cm3/mol Electrical resistivity: 0.0762 10-6/cm 
Thermal conductivity: 0.353 W/cmK Enthalpy of atomization: 163.2 kJ/mol Enthalpy of vaporization: 144.0 kJ/mol Enthalpy of fusion: 8.30 kJ/mol Specific heat capacity: 0.30 J/gK |
Energy levels: 2-8-18-8-2
Electron configuration: [Kr]5s2 Crystal Structure: Cubic face centered Atomic radius: 2.45 Å Covalent radius: 1.91 Å Oxidation States: +2 Electronegativity, Pauling: 0.95 Electron affinity: 0.048 eV First ionization energy: 5.695 eV 2nd ionization energy: 11.03 eV 3rd ionization energy: 43.60 eV Polarizability: 27.6 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 76Sr | 75.9416 | 8.9 s |  + |
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| 77Sr | 76.9378 | 9.0 s | + |
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| 78Sr | 77.93218 | 2.7 m | + |
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| 79Sr | 78.92971 | 2.1 m | + |
3/2- | |
| 80Sr | 79.92453 | 1.77 h | + |
0+ | |
| 81Sr | 80.92322 | 23.3 m | +; EC |
1/2- | |
| 82Sr | 81.91840 | 25.36 d | EC | ||
| 83mSr | 5.0 s | IT | 1/2- | ||
| 83Sr | 82.91756 | 1.350 d | +; EC |
7/2+ | |
| 84Sr | 0.56(1) | 83.913426 | Stable | 0+ | |
| 85mSr | 1.127 h | IT; EC | 1/2- | ||
| 85Sr | 84.912936 | 64.85 d | EC | 9/2+ | |
| 86Sr | 9.86(1) | 85.909265 | Stable | 0+ | |
| 87mSr | 2.81 h | IT | 1/2- | ||
| 87Sr | 7.00(1) | 86.908882 | Stable | 9/2+ | |
| 88Sr | 82.58(1) | 87.905617 | Stable | 0+ | |
| 89Sr | 88.907455 | 50.52 d | - |
5/2+ | |
| 90Sr | 89.907738 | 29.1 y | - |
0+ | |
| 91Sr | 90.91020 | 9.5 h | - |
5/2+ | |
| 92Sr | 91.91098 | 2.71 h | - |
0+ | |
| 93Sr | 92.91394 | 7.4 m | - |
5/2+ | |
| 94Sr | 93.91537 | 1.25 m | - |
0+ | |
| 95Sr | 94.91931 | 25.1 s | - |
1/2+ | |
| 96Sr | 95.92165 | 1.06 s | - |
0+ | |
| 97Sr | 96.92615 | 0.42 s | - |
(1/2+) | |
| 98Sr | 97.92845 | 0.65 s | - |
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| 99Sr | 98.9333 | 0.27 s | - |
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| 100Sr | 99.9354 | 0.201 s | - |
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| 101Sr | 100.9405 | 0.115 s | - |
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| 102Sr | 101.9430 | 68 ms | - |
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Isolated by Davey by electrolysis in 1808; however, Adair Crawford in 1790 recognized a new mineral (strontianite) as differing from other barium minerals (baryta). Strontium is found chiefly as celestite (SrSO4) and strontianite (SrCO3). The metal can be prepared by electrolysis of the fused chloride mixed with potassium chloride, or is made by reducing strontium oxide with aluminum in a vacuum at a temperature at which strontium distills off. Three allotropic forms of the metal exist, with transition points at 235 and 540 °C. Strontium is softer than calcium and decomposes water more vigorously. It does not
absorb nitrogen below 380 °C. It should be kept under mineral oil to prevent oxidation. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares. Natural strontium is a mixture of four stable isotopes. Twenty-six other unstable isotopes and isomers, are known to exist. Of greatest importance is 90Sr with a half-life of 29 years. It is a product of nuclear fallout and presents a health problem. This isotope, is one of the best long-lived high-energy beta emitters known, and is used in SNAP (Systems for Nuclear Auxiliary Power) devices. These devices hold promise for use in space vehicles, remote weather stations, navigational buoys, etc., where a lightweight, long-lived, nuclear-electric power source is needed. The major use for strontium at present is in producing glass for color television picture tubes. It has also found use in producing ferrite magnets and in refining zinc. Strontium titanate is an interesting optical material as it has an extremely high refractive index and an optical dispersion greater than that of diamond. It has been used as a gemstone, but it is very soft.
It does not occur naturally.
LINKS: Minerals Containing Strontium Strontium Isotope Stratigraphy Strontium Isotopes: Materials and Methods USGS Minerals Information: Strontium Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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