Rubidium

Rubidium (chemical symbol: Rb) is a chemical element with atomic number 37. It belongs to the alkali metals, the first group of the periodic table, which includes lithium, sodium, potassium and caesium. Like other alkali metals, rubidium has one electron in its outer shell, which makes it react readily.

Pure rubidium is a silvery metal that is highly soft, with a melting point close to room temperature. When exposed to air it reacts quickly with oxygen, and with water it reacts vigorously and releases hydrogen. For this reason it is stored in oil or inert gas such as argon.

Physical and chemical properties

Rubidium readily loses its outer electron, becoming the Rb⁺ ion. This is why it appears mainly in the form of compounds such as those with chlorine or sulphate. When placed in a flame, it produces a reddish-violet colour, which is used in flame testing.

Extraction

Rubidium does not occur in nature in elemental form; it is always found in combined minerals. It is usually extracted from potassium and lithium ores, particularly lepidolite and pollucite, and also from mineral-rich waters. Because there is no ore specific to rubidium, extraction is often a byproduct of lithium processing.

Isotopes

Natural rubidium consists of two isotopes: Rb-85, which is stable, and Rb-87, which is radioactive with a very long half-life. The decay of Rb-87 to strontium-87 is the basis of rubidium–strontium dating, a method used in geology to determine the age of rocks.

Applications

The applications of rubidium are limited and technical. It is used in atomic clocks that synchronize telecommunications networks and navigation systems. It is also used in physics research for laser cooling and certain specialized devices, and in some handheld space instruments.