Strontium is a chemical element with symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when it is exposed to air. Strontium has physical and chemical properties similar to those of its two neighbors calcium and barium. It occurs naturally in the minerals celestine and strontianite. While natural strontium is stable, the synthetic 90Sr isotope is present in radioactive fallout and has a half-life of 28.90 years.Symbol: Sr
Atomic number: 38
Electron configuration: Kr 5s2
Electrons per shell: 2,8,18,8,2
Atomic mass: 87.62 ± 0.01 u
Discoverer: William Cruickshank