All practice pages/Interatomic theory/Elements
Element 38, an alkaline earth metal
The element that makes fireworks red, named after a village in the Scottish Highlands.
Period 5, group 2. The other alkaline earth metals are tinted, and every cell opens its own article.
Strontium has 38 electrons, one for every proton, so the atom carries no charge. Below are the same 38 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s²
Short form: [Kr] 5s², where [Kr] stands for the 36 electrons krypton already has.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 3 here is 3s² 3p⁶ 3d¹⁰, and 2 + 6 + 10 is 18.
Strontium sits in period 5 and has 5 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones strontium can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 2 means 2.
Two valence electrons, which strontium gives up to form the Sr²⁺ ion in its compounds.
Mined as celestine (SrSO₄), mostly in Spain, China and Mexico, and as strontianite (SrCO₃).
Adair Crawford and William Cruikshank recognized in 1790 that a mineral from the lead mines at Strontian, Scotland, contained a new earth. Humphry Davy isolated the metal in 1808 by electrolysis.
Red fireworks and emergency flares, glow-in-the-dark paints and toys (strontium aluminate), ferrite magnets in small motors and speakers, and toothpaste for sensitive teeth. It was once added to the glass of television tubes to block X-rays, and strontium clocks are among the most precise clocks ever built.