Strontium

Strontium is an alkaline earth metal ([Kr]5s2) that gives up its two outer electrons to form Sr2+. Sitting between calcium and barium in group 2, it is more reactive than calcium: it tarnishes yellow in air and reacts readily with water. Because Sr2+ is close in size and charge to Ca2+, the body treats strontium like calcium and deposits it in bones and teeth. That makes radioactive strontium-90 from nuclear fallout a particular hazard, while stable strontium has been studied as a treatment for weak bones.

Strontium salts burn with a brilliant crimson flame, as excited strontium species emit red light, which is why they color fireworks and road flares. For decades the biggest use of strontium was in the glass of color television tubes, where it blocked X-rays; flat screens ended that market. Strontium ferrite is used in cheap permanent magnets, and strontium aluminate is the pigment in modern glow-in-the-dark products. Strontium atoms also power optical lattice clocks, among the most precise timekeepers ever built.

Discovery

In 1790 Adair Crawford and William Cruickshank recognized that a mineral from the lead mines near Strontian, in the Scottish Highlands, was different from the barium minerals it resembled; it became known as strontianite. Thomas Charles Hope studied the new earth further and noted its red flame. Humphry Davy isolated the metal by electrolysis in 1808 and named it after the village.