Strontium

Strontium
Name	Strontium
Number	38
Category	Alkaline earth metal
Appearance	silvery white metallic; with a pale yellow tint
Atomic weight	87.62
Electron configuration	[Kr] 5s2
Phase	solid
Melting point degC	777
Boiling point degC	1377
Density g cm3	2.64

Strontium is a soft, silvery-yellow alkaline earth metal with the chemical symbol Sr and atomic number 38. It is chemically similar to its group neighbors calcium and barium, readily oxidizing in air and reacting vigorously with water. The element is best known for the brilliant red color its salts impart to flames and fireworks, and for the radioactive isotope strontium-90, a significant byproduct of nuclear fission.

Properties

Strontium is a malleable and ductile metal that assumes a face-centered cubic crystalline structure at room temperature. It exhibits typical metallic properties, being a good conductor of electricity and heat. Chemically, it is highly reactive, tarnishing rapidly in air to form a dark oxide layer and reacting with water to produce strontium hydroxide and hydrogen gas. Its most common oxidation state is +2, and its compounds, such as strontium nitrate and strontium carbonate, often share solubility trends with those of barium but are more akin to calcium in their biological behavior. The element's flame test produces a characteristic crimson-red color, a property utilized in pyrotechnics and analytical chemistry.

History

The mineral strontianite, found near the Scottish village of Strontian in Argyll, was first distinguished from baryte by Adair Crawford in 1790. In 1791, Thomas Charles Hope conducted further experiments on the mineral, confirming it contained a new "earth." The metal itself was first isolated in 1808 by Sir Humphry Davy using the then-novel process of electrolysis on a mixture containing strontium chloride and mercuric oxide. Davy announced his discovery in a lecture to the Royal Society in London. The element was named after the village of its discovery, cementing the connection between Strontian and the new metal.

Occurrence and production

Strontium is the 15th most abundant element in the Earth's crust, occurring at an average concentration of about 370 parts per million. It is found primarily in the minerals celestine (strontium sulfate) and strontianite (strontium carbonate). Major deposits of celestine are mined in countries such as Spain, Mexico, China, and Iran. The primary method for producing metallic strontium is the thermite reduction of strontium oxide with aluminium under vacuum conditions. More commonly, strontium is processed into chemical compounds; strontium carbonate is often produced by treating celestine with sodium carbonate in the Black Ash process.

Applications

The largest historical use of strontium was in the production of cathode ray tube glass for color televisions to block X-ray emission. While this application has declined, strontium carbonate and other compounds remain important in the manufacture of ferrite magnets for applications like loudspeakers and microwave ovens. Strontium aluminate is a key component in long-lasting phosphors used in glow-in-the-dark paints and emergency signage. In pyrotechnics, strontium salts like the nitrate and carbonate are essential for producing deep red flames. Strontium ranelate was once used as a pharmaceutical for treating osteoporosis in the European Union.

Biological role and precautions

Non-radioactive strontium behaves similarly to calcium in biological systems and can be incorporated into bones. While not an essential nutrient, some studies suggest it may support bone density. The significant hazard arises from the radioactive isotope strontium-90, a fission product from events like nuclear weapon tests and accidents at facilities like Chernobyl and Fukushima Daiichi. Due to its chemical similarity to calcium, strontium-90 can be absorbed into the body and deposited in bone and bone marrow, posing a risk of bone cancer and leukemia. This was a major concern during the period of atmospheric nuclear testing in the mid-20th century, leading to extensive studies by organizations like the United States Atomic Energy Commission.

Isotopes

Naturally occurring strontium is composed of four stable isotopes: strontium-84, strontium-86, strontium-87, and strontium-88, with Sr-88 being the most abundant. The ratio of strontium-87 to strontium-86 is a crucial tool in geology and archaeology for dating rocks and determining the provenance of ancient artifacts. Among its radioactive isotopes, strontium-90 is the most notable due to its yield in nuclear fission, a 29-year half-life, and its presence in nuclear fallout. It is a pure beta emitter and finds some use in radioisotope thermoelectric generators for remote power, such as those used in Soviet-era lighthouses in the Arctic.

Category:Chemical elements Category:Alkaline earth metals