- Strontium (Sr) is an alkaline earth metal with atomic number 38, located in Group 2 of the periodic table between calcium and barium.
- It is a soft, silvery metal that tarnishes rapidly in air, forming a yellowish oxide layer.
- Strontium has two valence electrons in the 5s subshell, which it readily loses to form the +2 oxidation state, its only common ionic form. Its atomic structure consists of thirty-eight protons, typically fifty neutrons, and thirty-eight electrons arranged in five shells.
- Naturally occurring strontium is composed of four stable isotopes: strontium-84 (⁸⁴Sr, 0.56%), strontium-86 (⁸⁶Sr, 9.86%), strontium-87 (⁸⁷Sr, 7.00%), and strontium-88 (⁸⁸Sr, 82.58%). The isotope strontium-87 is radiogenic, produced by the decay of rubidium-87, and is important in geological dating methods. Radioactive strontium-90 (⁹⁰Sr), a fission product of nuclear reactions, is a significant environmental concern due to its long half-life (28.8 years) and high biological uptake.
- Strontium occurs naturally in the Earth’s crust at about 370 parts per million, making it more abundant than copper. It is never found in pure metallic form due to its reactivity, but is commonly found in the minerals celestine (SrSO₄) and strontianite (SrCO₃). Large deposits are found in China, Mexico, Spain, and Argentina. Commercially, strontium is extracted from celestine through reduction with coke or conversion to strontium carbonate.
- The element was discovered in 1790 by Scottish chemist Adair Crawford, who identified a new mineral from the village of Strontian in Scotland. Metallic strontium was first isolated in 1808 by Sir Humphry Davy through the electrolysis of strontium salts. The element was named after its place of discovery.
- Historically, strontium compounds—particularly strontium nitrate—were used to produce the brilliant red color in fireworks and signal flares. Strontium salts have also been used in ceramic glazes, pigments, and in the glass for color television cathode-ray tubes to block harmful X-ray emissions. Modern applications include ferrite magnets made from strontium ferrite (SrFe₁₂O₁₉) used in loudspeakers, motors, and data storage devices, as well as in pyrotechnics, zinc refining, and in producing specialized alloys.
- In medicine, strontium ranelate has been used in the treatment of osteoporosis, as it can stimulate bone formation and reduce bone resorption. Strontium naturally mimics calcium in biological systems, and stable isotopes are not considered toxic in small amounts. However, radioactive isotopes, especially ⁹⁰Sr, pose severe health risks because they can replace calcium in bones, leading to long-term radiation exposure and increased cancer risk.
- Chemically, strontium reacts vigorously with water to form strontium hydroxide (Sr(OH)₂) and hydrogen gas. It burns in air to form strontium oxide (SrO) and strontium nitride (Sr₃N₂). Its compounds are generally soluble in water and share similar chemistry with calcium and barium, though strontium tends to form more soluble salts.
- From an environmental perspective, stable strontium is not considered hazardous, but ⁹⁰Sr from nuclear fallout and reactor accidents is a serious contaminant due to its mobility in ecosystems and its tendency to bioaccumulate in bones and teeth. Environmental monitoring programs routinely measure strontium isotopes to assess nuclear contamination.
