Atomic Number: 37
Atomic Symbol: Rb
Atomic Weight: 85.4678
Electron Configuration: [Kr]5s¹
Atomic Radius: 247.5 pm
Melting Point: 39.3 C
^{Oxidation States: 1}


The name is derived from the Latin "rubidus", or "deepest red".
The element gives a reddish-violet color to a flame, hence its name. Honestly, I chose this element because it has one of the best names of any element.
Rubidium is very reactive, and is a very soft metal. It has been reported to ignite spontaneously in air. Also, it reacts violently with water, like the other Group 1 elements. The hydrogen released in a water reaction may ignite, if enough energy is released. Though this is only my opinion, I postulate that perhaps water vapor in the air may react with the rubidium, resulting in the reported spontaneous reaction. But of course, that's only an idea.
This element is, at the moment, considered to be the 16th most abundant element in the Earth's crust. Rubidium has many applications. There is a potential application in thin-film batteries and other electrical uses, because RbAg4I5 has the highest room conductivity of any known ionic crystal. At 20oC its conductivity is about the same as dilute sulfuric acid. It is also used as a "getter" in vacuum tubes (that is, it is used to bind any gas that enters into a vacuum tube). Also, Rubidium can do many things that its "cousin" Cesium can do. Like Cesium, it can be used as the resonant element in atomic clocks (clocks that are far more accurate than our digital wristwatches, which use silicon in the form of quartz as the resonant element.) Also like Cesium, it has a potential application in ion propulsion engines (for space shuttles). Other applications include laser cooling, use in fireworks (to give a purple color), and an ingredient in special uses of glass. Rb-87 is known as an alternative to Carbon in carbon-dating, because of its long half-life.
Rubidium occurs naturally in the minerals leucite, pollucite, and zinnwaldite, which contains traces of up to 1% of its oxide. Lepidolite contains 1.5% rubidium and this is the commercial source of the element. Rubidium's most common compounds are RbCl, RbF, and Rb2SO4.
Links: http://periodic.lanl.gov/elements/37.html
http://www.webelements.com/webelements/elements/text/Rb/key.html
http://environmentalchemistry.com/yogi/periodic/Rb.html
http://en.wikipedia.org/wiki/Rubidium