Strontium

Strontium is an alkaline earth metal discovered in 1808 by Humphry Davy. It is a reactive element and has various useful radioactive isotopes.

History and Discovery

Strontium was discovered earlier from mineral of barium (barium carbonate) by Adair Crawford in 1798. Strontium was formally discovered by Humphry Davy in 1808. This element was named after the place where its mineral was discovered, Strontian, a village in Scotland [1]. Strontium was used to produce sugar in the 19th century [2]. Large scale production of strontium was started due to its high demand and use in making television tube (cathode ray tubes) and its demand dramatically decreased with advancements in methods to make display screens and tubes.

Strontium

Periodic Table ClassificationGroup 2
Period 5
State at 20CSolid
ColorSilvery white metallic; with a pale yellow tint
Electron Configuration[Kr] 5s2
Electron Number38
Proton Number38
Electron Shell2, 8, 18, 8, 2
Density2.54 g.cm-3 at 20°C
Atomic number38
Atomic Mass87.62 g.mol -1
Electronegativity according to Pauling0.95

Occurrence

Strontium is quite abundant element and is ranked as the 15th most abundant element in the earth’s crust (about 0.034 %) [3]. Strontium is not present in native elemental form. It exists only in the form of compounds with other metals. the most common minerals of strontium are strontianite (strontium carbonate), celestite (strontium sulfate). Strontium is also present in ocean water with a ratio of 8mg/L. The largest deposits of strontium are found in China, Spain and Mexico.

Physical Characteristics

Strontium is a silvery white metal with a yellowish tint. It is characterized as an alkaline earth metal. It is soft metal and has a density of around 2.64 g/cm3. Strontium burns with a distinctive red color flame. There are three allotropic forms of strontium. Strontium has a considerably high refractive index. Strontium readily dissolves in liquid ammonia and forms a dark blue solution [4].

Chemical Characteristics

Strontium is highly reactive. It reacts with air to forms yellowish strontium oxide. Strontium readily reacts with water to form strontium hydroxide. Strontium reacts with nitrogen at high temperature, above 380°C. In powdered form, strontium undergoes spontaneous ignition (is pyrophoric) when exposed to air. Strontium is stored in kerosene or mineral oil to increase its shelf life and avoid reaction with water or air.

Significance and Uses

  • Strontium is widely used in the manufacturing of aerosol paints.
  • Strontium is used to make fireworks (pyrotechnics) for industrial and military purposes, including oxygen candles, safety matches and explosive bolts.
  • Chloride of strontium are used in manufacturing of medicinal toothpastes for sensitive teeth.
  • Strontium is used to make high quality pottery glaze.
  • Radioactive isotope of strontium (strontium-90) is used in nuclear power plants, spacecrafts and satellites as power generators (radioisotope thermoelectric generator RTGs).
  • Strontium-89 (radioactive isotope) is used in prostate cancer therapy to treat bone pain as the primary ingredient in medicine called Metastron.
  • Strontium is also used in the treatment of osteoporosis (strontium ranelate).

Health Hazards

Strontium is highly similar to calcium, and that is why it is absorbed in bone in place of calcium. This retention in body is mostly harmless as stable forms of strontium do not cause any health hazard. However, radioactive isotope, strontium-90 can lead to bone cancer. The Chernobyl nuclear incident (1986) is the most tragic example of radiation contamination as it polluted around 30,000 km2 of area with greater than 10 kBq/m2 of strontium-90 [5].

Isotopes of Strontium

There are sixteen naturally occurring isotopes of strontium. Naturally occurring strontium has four stable isotopes: strontium-84, strontium-86, strontium-87 and strontium -88. The most abundant stable isotope is strontium-88 (82.58 %). Strontium-87 is thought to be produced during the Big Bang and is also obtained during the radioactive decay of rubidium. The radioactive isotope, strontium-90 is produced as a byproduct of nuclear fission reaction.

REFERENCES

[1]. Murray, W. H. (1977). The Companion Guide to the West Highlands of Scotland. London: Collins. ISBN 0-00-211135-7.

[2]. Heriot, T. H. P (2008). “strontium saccharate process”. Manufacture of Sugar from the Cane and Beet. ISBN 978-1-4437-2504-0

[3]. Turekian, K. K.; Wedepohl, K. H. (1961). “Distribution of the elements in some major units of the Earth’s crust”. Geological Society of America Bulletin. 72 (2): 175–92. Bibcode:1961GSAB…72..175T. doi:10.1130/0016-7606(1961)72[175:DOTEIS]2.0.CO;2.

[4]. Greenwood and Earnshaw, pp. 112–13

[5]. “Chernobyl: Assessment of Radiological and Health Impact, 2002 update; Chapter I – The site and accident sequence” (PDF). OECD-NEA. 2002. Retrieved 3 June 2015