All practice pages/Interatomic theory/Elements
Element 37, an alkali metal
A metal that melts on a hot day, catches fire in air, and keeps time in satellites and cell towers.
Period 5, group 1. The other alkali metals are tinted, and every cell opens its own article.
Rubidium has 37 electrons, one for every proton, so the atom carries no charge. Below are the same 37 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹
Short form: [Kr] 5s¹, 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.
Rubidium sits in period 5 and has 5 shells. The period number counts the shells.
The outer shell holds 1 electron. Those are the ones rubidium 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 1 means 1.
One valence electron, which rubidium gives up easily to form the Rb⁺ ion. Like the other alkali metals, it reacts with water.
More abundant in the crust than copper or zinc, but scattered through minerals such as lepidolite and pollucite with no ores of its own. It is recovered as a byproduct of lithium and cesium production.
Robert Bunsen and Gustav Kirchhoff found it in 1861 with their new spectroscope, in the mineral lepidolite, a year after they found cesium the same way. They named it from the Latin rubidus, deep red, for the color of its brightest spectral lines.
Atomic clocks, including many in GPS satellites and cell towers, and research on ultracold atoms: the first Bose-Einstein condensate, made in 1995, was a cloud of rubidium atoms. It also goes into photocells and specialty glass, and rubidium-strontium dating measures the age of rocks.
Catches fire on its own in air and reacts explosively with water, so it is sealed in glass under argon or oil.