Strontium
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Background
Strontium is a silvery-yellow, metallic element. Its atomic number is 38 and its symbol is Sr. It is a relatively soft element.
Strontium was first discovered in 1790 by the Scottish scientist Adair Crawford who was studying samples of a new mineral. This new mineral, strontianite, is now known to be composed of strontium carbonate, SrCO3. Crawford determined that this new mineral contained an element that had never been recognized before, which he identified and called strontium. Pure strontium was not isolated until 1808.
Strontium belongs to a group of elements known as the alkali earth metals. Like other alkali metals, it is chemically active and will react with both air and water.
Two radioactive isotopes of strontium, Strontium-89 and –90, are created by atomic bomb explosions and are found in their radioactive fallout. This radioactive strontium is absorbed by the body and replaces calcium in the bones. Once they become part of the bone, they remain there for the lifetime of the organism, giving off radiation.
There is no biological benefit to strontium.
Name
| Previous Element: Nitrogen Strontium Next Element: Fluorine |
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| Physical Properties | ||
|---|---|---|
| Color | silvery | |
| Phase at Room Temp. | {{{state25C}}} | |
| Density (g/cm3) | 2.63 | |
| Hardness (Mohs) | 1.8 | |
| Melting Point (K) | 1042.2 | |
| Boiling Point (K) | 1654 | |
| Heat of Fusion (kJ/mol) | 9.205 | |
| Heat of Vaporization (kJ/mol) | 139 | |
| Heat of Atomization (kJ/mol) | 164 | |
| Thermal Conductivity (J/m sec K) | 35.4 | |
| Electrical Conductivity (1/mohm cm) | 43.478 | |
| Pure Cost ($/100g) | $ 100.00 | |
| Bulk Cost ($/100g) | --- | |
| Source | Celestite (sulfide) | |
| Atomic Properties | ||
| Electron Configuration | [Kr]5s2 | |
| Number of Isotopes | 4 | |
| Electron Affinity (kJ/mol) | --- | |
| First Ionization Energy (kJ/mol) | 549.5 | |
| Second Ionization Energy (kJ/mol) | 1064.2 | |
| Third Ionization Energy (kJ/mol) | 4206.7 | |
| Electronegativity | 0.95 | |
| Polarizability (Å3) | 27.6 | |
| Atomic Weight | 87.62 | |
| Atomic Volume (cm3/mol) | 33.3 | |
| Ionic Radius2- (pm) | --- | |
| Ionic Radius1- (pm) | --- | |
| Atomic Radius (pm) | 215 | |
| Ionic Radius1+ (pm) | --- | |
| Ionic Radius2+ (pm) | 132 | |
| Ionic Radius3+ (pm) | --- | |
| Common Oxidation Numbers | +2 | |
| Other Oxid. Numbers | ||
| Abundance | ||
| In Solar System (log) | 1.371 | |
| In Earth's Crust (mg/kg) | 3.70×102 | |
| In Earth's Ocean (mg/L) | 7.9 | |
| In Human Body (%) | 0.0005 % | |
| Regulatory / Health | ||
| CAS Number | 7440-24-6 | |
| OSHA Permissible Exposure Limit (PEL) | No limits | |
| OSHA PEL Vacated 1989 | No limits | |
| NIOSH Recommended Exposure Limit (REL) | No limits | |
Named after the village of "Strontian" in Scotland.
Sources
Strontium is recovered from two strontium minerals, strontianite (strontium carbonate) and celestite (strontium sulfate). The most common of these two minerals is celestite. Strontium minerals have not been mined in the United States since 1959. Consequently, U.S. companies import 100% of the strontium minerals needed for strontium. They are imported exclusively from Mexico. In addition, strontium compounds are imported from Mexico (90%) and Germany (9%) and 1% from other nations.
Worldwide resources of strontium minerals have not been completely studied. However, experts estimate that world resources of strontium exceed 1 billion tons.
Uses
Most strontium (76% of the strontium consumed each year) is used to make compounds that are applied to the glass picture tubes on color television sets. This compound blocks the X-rays created by the picture tube.
Some strontium (10%) is used to make special magnets called ferrite ceramic magnets.
Strontium is the element that gives road flares and fireworks a bright red color. Pyrotechnics and flares account for 5% of the annual strontium consumption.
Substitutes and Alternative Sources
There are a few elements that can be used in place of strontium for some of its applications. There are two possible problems with such a substitution. First, no element or compound works as well as strontium in these applications. Second, the possible substitutes can be more expensive than strontium.
Further Reading
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
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