Red, White, Blue

Last night, Palladian was asking about neutrons in the context of blue which naturally led to a late night discussion of how neutrons protect us from being blown up.

Here's a story of another color -- red -- including explosions, isotopes, unpaired electrons, and radioactivity.

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The name rubidium derives from "deep red" in Latin. Robert Bunsen (yes, that Bunsen) named the element after he and physicist Gustav Kirchoff discovered it burning reddish-purple in a flame. They also found cesium which lies directly below (rhymes with) rubidium and which burned brightly blue (cesium derives from the Latin word for blue).

Burning elements is still important in fireworks and also in modern analytical chemistry techniques such as ICP-MS. Also, a fair number of elements are named after their colors: chlorine, rubidium, cesium, chromium, rhodium, indium, iridium, iodine, etc.

The depiction above implies how weakly rubidum holds its outermost electron and why it so readily gives it up to become Rb⁺. Most anything can pluck it off. Here's a spectacular video of rubidium hitting water:

Naturally occurring rubidium has two isotopes: the stable ⁸⁵Rb (72.2%) and the radioactive ⁸⁷Rb (27.8%).  ⁸⁷Rb is considered only "slightly" radioactive--despite its abundance (it is naturally present in seawater)--because of its extremely long half-life of 10¹⁰ years.  Remember that something has to actually decay in order for it to emit radiation.