Rubidium
alkali metalProperties
| Property | Value |
|---|---|
| Atomic Mass | 85.468 amu |
| Category | alkali metal |
| Group | 1 |
| Period | 5 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 |
| Electronegativity | 0.82 (Pauling) |
| Oxidation States | 1 |
| Melting Point | 312.45 K (39.3 °C) |
| Boiling Point | 961 K (687.9 °C) |
| Density | 1.532 g/cm³ |
| Discovered By | Robert Bunsen, Gustav Kirchhoff (1861) |
About Rubidium
Rubidium was Bunsen and Kirchhoff's second flame-spectroscopy find — a year after cesium and using the same Heidelberg spectroscope, they spotted two deep red emission lines at 780.0 and 794.8 nm in lepidolite mica residues and named the new element from Latin rubidus, dark red. It's a soft alkali metal that melts at 39.3 °C in your hand, oxidizes instantly in air, and ignites on contact with water releasing hydrogen and forming RbOH. The single 5s electron makes it a classic +1 cation with chemistry that mirrors potassium's almost exactly, including the kidney's inability to distinguish Rb⁺ from K⁺ — which is why ⁸²Rb (76-second positron emitter from a strontium generator) is the workhorse PET tracer for cardiac perfusion. The other big role is metrology: the ⁸⁷Rb hyperfine ground-state transition at 6.834 GHz drives the chip-scale atomic clocks that keep GPS receivers honest, and laser-cooled ⁸⁷Rb formed the first Bose-Einstein condensate in Eric Cornell and Carl Wieman's JILA experiment in 1995.
Fun Fact
Rubidium was the first element to be discovered by flame spectroscopy in 1861, and rubidium-87 atoms cooled to near absolute zero were used to create the first Bose-Einstein condensate in 1995, a new state of matter predicted by quantum mechanics.
Common Uses
- Hyperfine 6.834 GHz reference in chip-scale atomic clocks for GPS and 5G timing
- ⁸²Rb perfusion tracer in cardiac PET imaging from Sr-82/Rb-82 generators
- Laser-cooled ⁸⁷Rb in Bose-Einstein condensate and atom-interferometry experiments
- Photoemissive cathodes in vacuum-tube photomultipliers for low-light detection
- Getter alloy for residual oxygen and water removal in sealed vacuum tubes
- Heat-transfer fluid candidate for high-temperature thermoelectric generators