Strontium Facts – Element 38 or Symbol Sr

Strontium is a chemical element with the symbol Sr and atomic number 38. It is an alkaline earth metal that is soft and silver-white when freshly cut, but tarnishes to a yellowish color in air. Strontium is chemically similar to its group neighbors, calcium and barium. In everyday life, strontium occurs in red fireworks, road flares, toothpaste, and the mineral celestine.

Basic Strontium Facts

• Name: Strontium
• Atomic Number: 38
• Element Symbol: Sr
• Atomic Mass: 87.62
• Element Group: Group 2 (alkaline earth metals)
• Period: Period 5
• Block: s-block
• Electron Configuration: [Kr] 5s²
• Appearance: Solid silvery metal with pale golden oxidation

Discovery, Naming, and Isolation

Strontium was discovered in the village of Strontian in Scotland in 1790 by Adair Crawford and William Cruickshank. Crawford and Cruickshank discovered an ore from the lead mines in the area that had new properties. They named it strontianite. Humphry Davy first isolated strontium in 1808 by electrolysis of strontium chloride. The element gets its name for the village, combined with the -ium suffix of other alkaline earth element names.

Strontium Appearance and Properties

Strontium is a bright silvery metal that is highly reactive. It quickly oxidizes in air so that it appears golden, but eventually appears dark. Storing the metal in an inert atmosphere preserves its true color. Strontium reacts with water to produce strontium hydroxide and hydrogen gas. Strontium compounds burn with a characteristic bright red flame. The pure metal is softer than calcium but harder than barium. The element exists in three forms or allotropes.

Element Group

Strontium is part of the alkaline earth metals group, which also includes beryllium, magnesium, calcium, barium, and radium. These metals all have two electrons in their outer shell and typically exhibit a +2 oxidation state.

Natural and Synthetic Isotopes

Strontium has four stable, naturally occurring isotopes: ⁸⁴Sr, ⁸⁶Sr, ⁸⁷Sr, and ⁸⁸Sr. The most abundant isotope is ⁸⁸Sr (82.58%). There are also several radioactive isotopes. The most notable radioisotopes are ⁸⁹Sr and ⁹⁰Sr. Stronium-89 has a half-life of 50.6 days and finds use in bone cancer treatment. Strontium-90 has a half-life of 28.90 years and is a fission product and component of radioactive fallout.

Abundance and Sources

Strontium is the 16th most abundant element in the Earth’s crust. It mainly occurs in the minerals celestite (SrSO₄) and strontianite (SrCO₃). The primary producers of the element are China, Spain, Mexico, Argentina, and Morocco. While the ore occurs in the United States, it hasn’t been mined since the 1950s.

Purification

Strontium purification involves converting the sulfate into a carbonate, followed by reduction of strontium oxide (SrO) with aluminum in a vacuum.

Uses of Strontium

Previously, around 75% of strontium went to glass for color television cathode-ray tubes for preventing x-ray emission. Now other types of displays are common, so uses of the element have shifted:

1. Alloying Agent: Strontium improves the casting properties of aluminum alloys.
2. Pyrotechnics: Strontium compounds produce deep red colors in fireworks.
3. Ferrite Magnets: The element is a component of ferrite magnets in electric motors and generators.
4. Medical: The isotope ⁸⁹Sr treats bone pain associated with cancer. Isotopes are tracers for studying bone formation and resorption. The drug strontium ranelate improves bone growth and density, although it also increases the risk of cardiovascular disorders.
5. Toothpaste: Strontium chloride hexahydrate is an ingredient in toothpaste for reducing tooth sensitivity.
6. Metal Refining: Strontium helps remove lead impurities during zinc refining.
7. Sugar Refining: Strontium hydroxide aids in sugar crystal refining of sugar beets.
8. Road Flares: Strontium nitrate in road flares acts as an oxidizer and provides a bright red light.
9. Environmental Tracing: Strontium isotopes trace the origins of water and sediments.
10. Glass Manufacturing: Strontium oxide improves the optical properties of glass.

Oxidation States and Main States

Strontium commonly exhibits a +2 oxidation state, which is typical for group 2 elements. Less commonly, it displays the +1 oxidation state.

Biological Role, Health Effects, and Toxicity

Strontium has no known biological role in the human body. It is generally considered non-toxic. However, radioactive isotopes are extremely dangerous, increasing the risk of bone cancer and leukemia. Since strontium replaces calcium, too much exposure in children leads to bone growth issues. The element accumulates in the human body over time.

Some marine radiolarians (a type of protozoa) make mineral skeletons using strontium sulfate.

Table of Key Strontium Facts

References

• Angino, Ernest E.; Billings, Gale K.; Andersen, Neil (1966). “Observed variations in the strontium concentration of sea water”. Chemical Geology. 1: 145. doi:10.1016/0009-2541(66)90013-1
• Bauman, Glenn; Charette, Manya; Reid, Robert; Sathya, Jinka (2005). “Radiopharmaceuticals for the palliation of painful bone metastases – a systematic review”. Radiotherapy and Oncology. 75 (3): 258.E1–258.E13. doi:10.1016/j.radonc.2005.03.003
• Davy, H. (1808). “Electro-chemical researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia”. Philosophical Transactions of the Royal Society of London. 98: 333–70. doi:10.1098/rstl.1808.0023
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Murray, T. (1993). “Elementary Scots: The Discovery of Strontium”. Scottish Medical Journal. 38 (6): 188–89. doi:10.1177/003693309303800611