|Name, symbol||Rubidium, Rb|
|Rubidium in the periodic table|
|Standard atomic weight (Ar)||85.4678(3)|
|Group, block||(alkali metals); s-block|
|Electron configuration||[Kr] 5s1|
|2, 8, 18, 8, 1|
|Melting point||312.45 K (39.30 °C, 102.74 °F)|
|Boiling point||961 K (688 °C, 1270 °F)|
|Density near r.t.||1.532 g/cm3|
|when liquid, at||1.46 g/cm3|
|Triple point||312.41 K, kPa|
|Critical point||2093 K, 16 MPa (extrapolated)|
|Heat of fusion||2.19 kJ/mol|
|Heat of||69 kJ/mol|
|Molar heat capacity||31.06 J/(mol·K)|
|Oxidation states||+1, −1 (a strongly basic oxide)|
|Electronegativity||Pauling scale: 0.82|
1st: 403 kJ/mol |
2nd: 2632.1 kJ/mol
3rd: 3859.4 kJ/mol
|Atomic radius||empirical: 248 pm|
|Covalent radius||220±9 pm|
|Van der Waals radius||303 pm|
|Crystal structure||Body-centered cubic (bcc)|
|Speed of sound thin rod||1300 m/s (at 20 °C)|
|Thermal expansion||90 µm/(m·K)|
|Thermal conductivity||58.2 W/(m·K)|
|Electrical resistivity||128·10-9 Ω·m (at 20 °C)|
|Young's modulus||2.4 GPa|
|Bulk modulus||2.5 GPa|
|Brinell hardness||0.216 MPa|
|CAS Registry Number||7440-17-7|
|Discovery||Robert Bunsen and Gustav Kirchhoff (1861)|
|First isolation||George de Hevesy|
Rubidium is an alkali metal with the chemical symbol Rb and an atomic number of 37. It is a relatively rare element due to its even distribution through the Earth's crust. It does not have any known ores with a concentration higher than 1%. The world production of rubidium compounds is between 2-4 tonnes per year.
Rubidium will react quickly and violently with water producing rubidium hydroxide and hydrogen. It also reacts violently with halogens in the presence of small amounts of water to form the corresponding halides.
Rubidium is a soft, silvery metal which will tarnish quickly in air. It has a relatively low melting point of 39°C. Like other alkali metals, it is quite soft and can easily be cut with a steel blade.
Rubidium metal is highly reactive and shipping regulations are very strict. It is offered by element dealers such as Metallium at very high prices(~$150/g). Rubidium salts are also available to the public on sites like eBay, priced at around $3/g.
Rubidium metal can be prepared by the dry distillation of a rubidium halide and lithium metal, yielding rubidium vapor due to its low boiling point. This low boiling point is responsible for shifting the equilibrium of this reaction; the vapor can then be condensed in a glass vessel. This is quite dangerous and the risk of explosion is very high. It must be done in an inert atmosphere to prevent the spontaneous oxidation and ignition of the rubidium vapor at the high reaction temperatures.
- Make rubidium hydroxide
- Rubidium suboxides
- Colored flash powders with rubidium salts
Rubidium metal is extremely dangerous as it will catch fire in moist air and explode on contact with water. Upon long term storage in mineral oil, it will react with air to form shock sensitive explosive peroxides, similar to potassium. In its ionic form, rubidium ions are extremely similar to potassium ions, and replace them throughout the body. Due to their similarity, this caused no ill effects in study participants with 100x the normal amount (0.36g) of rubidium in a human. Mice were able to survive with significant fractions of potassium in their bodies replaced with rubidium, but when the rubidium:potassium ratio approached 1:1, the mice died.
Rubidium can be stored in mineral oil, but since rubidium is much more reactive than sodium or potassium, it will oxidize much faster. It's best stored under inert atmosphere, such as argon. For long term storage, it should be sealed in a glass ampoule.
Since rubidium is expensive, it is best recycled if possible. However, rubidium ions are not toxic to the environment and moderate amounts may be discarded in municipal waste.