Rubidium has the atomic number 37, and its atomic symbol is Rb.

Rubidium is an alkali metal in the same group as lithium, sodium, and potassium.

It is soft enough to be cut with a knife.

Rubidium is silvery white in appearance but tarnishes quickly when exposed to air.

It is highly reactive, especially with water.

Rubidium has a melting point of 39.3°C (102.7°F), allowing it to melt in your hand if held briefly.

It is more reactive than potassium but less reactive than cesium.

Rubidium is not found in its pure form in nature because of its reactivity.

It was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff in Germany.

Its name comes from the Latin word “rubidus,” meaning deep red, in reference to the bright red spectral lines it produces.

Rubidium was discovered through spectroscopy by observing its distinct red emission lines.

It was identified shortly after cesium, another alkali metal, using similar spectroscopic methods.

Rubidium is one of the softest metals, slightly harder than cesium.

It is extremely reactive, especially with water, producing rubidium hydroxide and hydrogen gas.

Rubidium reacts readily with air and moisture and is typically stored under mineral oil.

It can ignite spontaneously in air when finely divided.

Rubidium has two naturally occurring isotopes: Rb 85 and Rb 87.

Rb 87 is radioactive, with a half life of about 49 billion years.

Rubidium forms ionic compounds such as rubidium chloride (RbCl).

It forms alloys with potassium, cesium, and sodium.

Rubidium has a low electronegativity of 0.82 on the Pauling scale.

Rubidium is used in atomic clocks, which are highly precise timekeeping devices. Rubidium atomic clocks are more accurate than standard quartz clocks, with extremely small errors over millions of years.

Rubidium is used in research involving Bose Einstein condensates.

Rubidium salts are used in specialized glasses for fireworks, creating violet colors.

Rubidium is used in photoelectric cells.

Rubidium vapor is used in laser cooling experiments.

Rubidium 87 is used to study magnetic fields in advanced physics research.

Rubidium can be used in ion engines for spacecraft propulsion.

Rubidium has limited medicinal application as a supplement in certain niche therapies.

Rubidium is used in vacuum tubes and electronics research.

Rubidium reacts with water even more violently than potassium.

Rubidium produces a purple flame when burned.

Rubidium compounds are typically colorless or white.

RbCl is highly soluble in water.

Rubidium has a low melting point for a metal, similar in behavior to mercury, although it remains solid at room temperature.

Rubidium can substitute for potassium in some biological systems, though it is not essential for humans.

Rubidium hydroxide is highly caustic.

Rubidium is found in small quantities in minerals such as lepidolite, pollucite, and carnallite.

The Earth’s crust contains about 90 parts per million rubidium.

Rubidium is more abundant than copper in the Earth’s crust.

It is often obtained as a byproduct of lithium extraction.

Rubidium is more common than silver in the Earth’s crust.