1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶ 5s²

Characteristics

Due to its extreme reactivity to air, this element occurs naturally only in compounds with other elements, as in the minerals Strontianite and Celestite.  Strontium compounds are useful in pyrotechnic devices and signal flares because of the bright crimson coloring they give to flames.

Strontium is a bright silvery metal that is softer than Calcium and even more reactive in water, which Strontium decomposes on contact with to produce Strontium Hydroxide and Hydrogen Gas.  It burns in air to produce both Strontium Oxide and Strontium Nitride, but since it does not react with Nitrogen below 380°C it will only form the oxide spontaneously at room temperature.  It should be kept under kerosene to prevent oxidation; freshly exposed Strontium metal rapidly turns a yellowish color with the formation of the oxide.  Finely powdered Strontium metal will ignite spontaneously in air.  Volatile Strontium salts impart a 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.

Occurrence

Strontium commonly occurs in nature, the 15th most abundant element on earth, averaging 0.034% of all igneous rock and is found chiefly as the form of the sulfate mineral Celestite (SrSO₄) and the carbonate Strontianite (SrCO₃).  Of the two, Celestite occurs much more frequently in sedimentary deposits of sufficient size to make development of mining facilities attractive.  Strontianite would be the more useful of the two common minerals because Strontium is used most often in the carbonate form, but few deposits have been discovered that are suitable for development.  The metal can be prepared by electrolysis of melted Strontium Chloride mixed with Potassium Chloride:

Sr²⁺ + 2 e^- Sr

2Cl^- Cl_{2 (g)} + 2 e^-

Alternatively it is made by reducing Strontium Oxide with Aluminum in a vacuum at a temperature at which Strontium distills off.  Three allotropes of the metal exist, with transition points at 235 and 540°C.  The largest commercially exploited deposits are found in England.

Applications

As a pure metal Strontium is being used in Strontium 90%-Aluminum 10% alloys of an eutectic composition for the modification of Aluminum-Silicon casting alloys.  The primary use for Strontium compounds is in glass for color television cathode ray tubes to prevent X-ray emission.

• ⁸⁹Sr is the active ingredient in Metastron, a radiopharmaceutical used for bone pain secondary to metastatic prostate cancer.  The Strontium acts like Calcium and is preferentially incorporated into bone at sites of increased osteogenesis.   This localization focuses the radiation exposure on the cancerous lesion.
• ⁹⁰Sr has been used as a power source fo RTGs.  ⁹⁰Sr produces about 0.93 watts of heat per gram (it is lower for the grade of ⁹⁰Sr used in RTGs, which is Strontium Fluoride.  However, ⁹⁰Sr has a lifetime approximately 3 times shorter and has a lower density than ²³⁸Pu, another RTG fuel.  The main advantage of ⁹⁰Sr is that it is cheaper than ²³⁸Pu and is found in nuclear waste.
• ⁹⁰Sr is also used in cancer therapy.  Its beta emission and long half-life is ideal for superficial radiotherapy.

Compounds

• Ferrite magnets and refining Zinc.
• Strontium Titanate has an extremely high refractive index and an optical dispersion greater than that of diamond, making it useful in a variety of optics applications.
• Strontium Titanate has been cut into gemstones, in particular for its use as diamond simulant.  However, it is very soft and easily scratches so it is rarely used.
• Strontium Carbonate, Strontium Nitrate, and Strontium Sulfate are commonly used in fireworks for red color.
• Strontium Aluminate is used as a bright phosphor with long persistence of phosphorescence. 
• Strontium Chloride is sometimes used in toothpastes for sensitive teeth.  One popular brand includes 10% Strontium Chloride Hexahydrate by weight.
• Strontium Oxide is sometimes used to improve the quality of some pottery glazes. 
• Strontium is also commonly used in aerosol paint, such as the Spanish Montana (Montana Hardcore).  This is one of the most likely sources of exposure to the public.

Isotopes

The alkali earth metal Strontium has four stable, naturally occurring isotopes: ⁸⁴Sr (0.56%), ⁸⁶Sr (9.86%), ⁸⁷Sr (7.0%) and ⁸⁸Sr (82.58%).  Only ⁸⁷Sr is radiogenic; it is produced by decay from the radioactive alkali metal ⁸⁷Rb, which has a half-life of 4.88 × 10¹⁰ years.  Thus, there are two sources of ⁸⁷Sr in any material: that formed during primordial nucleo-synthesis along with ⁸⁴Sr, ⁸⁶Sr and ⁸⁸Sr, as well as that formed by radioactive decay of ⁸⁷Rb.  The ratio ⁸⁷Sr/⁸⁶Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0.  Because Strontium has an atomic radius similar to that of Calcium, it readily substitutes for Ca in minerals.

Twenty-eight  unstable isotopes are known to exist. Of greatest importance is ⁹⁰Sr, it has a half-life of about 28.78 years and decays intoYttrium-90 through beta decay.  It is a by-product of nuclear fission which is found in nuclear fallout and presents a health problem since it substitutes for Calcium in bone, preventing expulsion from the body.  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 spacecraft, remote weather stations, navigational buoys, etc, where a lightweight, long-lived, nuclear-electric power source is required.  The 1986 Chernobyl nuclear accident contaminated a vast area with ⁹⁰Sr.    The strong radiation emitted by the isotope interferes with the production of new blood cells and can cause death.

Strontium was among the radioactive materials released by the 1957 Windscale fire.

Precautions

In its pure form Strontium is extremely reactive with air and spontaneously combusts.  It is therefore considered to be a fire hazard.

The Strontium unit is used in measuring radioactivity from absorbed ⁹⁰Sr.

The human body absorbs Strontium as if it were Calcium.  Due to the elements being sufficiently similar chemically, the stable forms of Strontium do not pose a significant health threat, but the radioactive 90Sr can lead to various bone disorders and diseases, including bone cancer.

An experimental drug made by combining Strontium with Ranelic Acid has aided in bone growth, boosted bone density and lessened fractures.  Women receiving the drug showed a 6.8% increase in bone density.  Women receiving a placebo had a 1.3% decrease.   Half the increase in bone density (measured by x-ray densitometry) is attributed to the higher atomic weight of Sr compared with Calcium, whereas the other half is assumed to be a true increase in bone mineral content.  Strontium Ranelate is registered for treatment of osteoporosis in Europe at a dose of 2 grams daily.

Several naturally occurring Strontium compounds have additionally been found to enhance bone growth and density and lessen the incidence of fractures, and efficacy of treatment has not been shown to vary significantly between various Strontium compounds.  These compounds include Strontium Lactate, Strontium Citrate, Strontium Carbonate and Strontium Gluconate.

(Strontian, town in Scotland) Isolated by Davy by electrolysis in 1808; however, Adair Crawford in 1790 recognized a new mineral (strontianite) as differing from other barium minerals. Strontium is found chiefly as celestite and strontianite. 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^oC. Strontium is softer than calcium and decomposes water more vigorously. It does not absorb nitrogen below 380^oC. It should be kept under kerosene 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. Sixteen other unstable isotopes 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 is very soft. It does not occur naturally. Strontium metal (98% pure) in January 1990 cost about $5/oz.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond

Strontium was discovered by Adair Crawford, an Irish chemist, in 1790 while studying the mineral witherite (BaCO₃). When he mixed witherite with hydrochloric acid (HCl) he did not get the results he expected. He assumed that his sample of witherite was contaminated with an unknown mineral, a mineral he named strontianite (SrCO₃). Strontium was first isolated by Sir Humphry Davy, an English chemist, in 1808 through the electrolysis of a mixture of strontium chloride (SrCl₂) and mercuric oxide (HgO). Today, strontium is obtained from two of its most common ores, celestite (SrSO₄) and strontianite (SrCO₃), by treating them with hydrochloric acid, forming strontium chloride. The strontium chloride, usually mixed with potassium chloride (KCl), is then melted and electrolyzed, forming strontium and chlorine gas (Cl₂).

Most of the strontium produced today is used in the manufacture of color television picture tubes. It is also used to refine zinc and is combined with iron to make magnets.

Two strontium compounds, strontium carbonate (SrCO₃) and strontium nitrate (Sr(NO₃)₂), burn with a bright, red flame and are used in fireworks and signal flares.   Strontium carbonate is also used to make certain kinds of glass and is the base material for making most other strontium compounds.

Strontium-90, a radioactive isotope of strontium, is a common product of nuclear explosions.  It has a half-life of about 28.8 years and decays intoYttrium-90 through beta decay.  Strontium-90 is especially deadly since it has a relatively long half-life, is strongly radioactive and is absorbed by the body, where it accumulates in the skeletal system. The radiation affects the production of new blood cells, which eventually leads to death.