Rubidium: the essentials
Rubidium can be liquid at ambient temperature, but only on a hot day given that its melting point is about 40°C. It is a soft, silvery-white metallic element of the alkali metals group (Group 1). It is one of the most most electropositive and alkaline elements. It ignites spontaneously in air and reacts violently with water, setting fire to the liberated hydrogen. As so with all the other alkali metals, it forms amalgams with mercury. It alloys with gold, caesium, sodium, and potassium. It colours a flame yellowish-violet.
Cartoon by Nick D Kim ([Science and Ink], used by permission).
Image adapted with permission from Prof James Marshall's (U. North Texas, USA) Walking Tour of the elements CD.
Rubidium: historical information
Rubidium was discovered in 1861 spectroscopically by Robert Bunsen and Gustav Kirchoff as an impurity associated with samples of the mineral lepidolite (a form of mica). The name rubidium (from the Latin "rubidus" - dark red) was coined for its bright red spectroscopic lines.
Rubidium salts were isolated by Bunsen by precipitation from spring waters - along with salts of other Group 1 elements. He was able to separate them and isolated the chloride and the carbonate. He isolated rubidium metal by reducing rubidium hydrogen tartrate with carbon.
Rubidium around us Read more »
Rubidium has no biological role but is said to stimulate the metabolism. It can accumulate ahead of potassium in muscle.
Rubidium is far too reactive to be found as the free metal in nature. It is relatively rare, although it is the 16th most abundant element in the earth's crust. Rubidium is present in some minerals found in North America, South Africa, Russia, and Canada. It is found in some potassium minerals (lepidolites, biotites, feldspar, carnallite), sometimes with caesium as well.
|Location||ppb by weight||ppb by atoms||Links|
|Human||4600 ppb by weight||340 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 312.46 [39.31 °C (102.76 °F)] K
- Boiling point: 961 [688 °C (1270 °F)] K
- Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of rubidium is: bcc (body-centred cubic).
Rubidium: orbital properties Read more »
Rubidium atoms have 37 electrons and the shell structure is 184.108.40.206.1. The ground state electronic configuration of neutral Rubidium is [Kr].5s1 and the term symbol of Rubidium is 2S1/2.
- Pauling electronegativity: 0.82 (Pauling units)
- First ionisation energy: 403.0 kJ mol‑1
- Second ionisation energy: 2633 kJ mol‑1
Isolation: rubidium would not normally be made in the laboratory as it is available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative rubidium ion Rb+.
Rubidium is not made by the same method as sodium as might have been expected. This is because the rubidium metal, once formed by electrolysis of liquid rubidium chloride (RbCl), is too soluble in the molten salt.
cathode: Rb+(l) + e- → Rb (l)
anode: Cl-(l) → 1/2Cl2 (g) + e-
Instead, it is made by the reaction of metallic sodium with hot molten rubidium chloride.
Na + RbCl ⇌ Rb + NaCl
This is an equilibrium reaction and under these conditions the rubidium is highly volatile and removed from the system in a form relatively free from sodium impurities, allowing the reaction to proceed.
Rubidium isotopes Read more »
|85Rb||84.911794 (3)||72.17 (2)||5/2||1.35303|
|87Rb||86.909187 (3)||27.83 (2)||3/2||2.75124|