PTL:Rubidium
From ChemEd Collaborative
Rubidium is a Group IA metal (or alkali metal) in the 5th period. Other members of the group are lithium (Li), sodium (Na), potassium (K), cesium (Cs), and francium (Fr).
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Discovered
The element was discovered in 1861 by Bunsen and Kirchhoff in lepidolite, a lithium mica, a mineral that remains its principal source.
Characteristics
It is the 16th most abundant element in the earth's crust. However, it is widely dispersed and not found as the principal component of any mineral.
It is a silvery, soft, ductile metal, and is the 4th lightest metallic element. It can be a liquid at room temperature (mp, 39°C). Like the other alkali metals, Rb metal has a body centered cubic structure.
Reactions
The chemical and physical properties of Rb are similar to K and Cs, but it is slightly more reactive than K. It reacts rapidly with air. When heated, it ignites spontaneously, burning with a violet flame (like K) and forming four oxides: a yellow monoxide (Rb2O); a dark brown peroxide (Rb2O2); a black trioxide (Rb2O3); and a dark orange superoxide (RbO2). It reacts violently with water (to liberate H2 and RbOH).
Uses
The uses of the element all depend on the fact that it is highly electropositive, that is, it is an excellent reducing agent. For this reason it has been used as a "getter" - a substance that reacts readily with, and therefore removes, O2 - in vacuum tubes. In addition, it is used as the electron source in [photocells].
The crystalline solid [[RbAg4I5]] is potentially important because it has the highest conductivity at room temperature of any known ionic solid.
Emission Spectrum
This is the visible emission spectrum for rubidium.
