Name rubidium
Symbol Rb
Atomic Weight 85.4678
Atomic Number 37
CAS ID 7440-17-7
Group Number 1
Group Name Alkali Metal
Period Number 5
Origin of Name Latin, rubidius = "deepest red."
Year Discovered 1861
Discovery Credits W. Noddack, Ida Tacke, and O. Berg in Berlin, Germany.
Class Metallic
Color Silvery White
Standard State Solid at 77 F & 298 K
Description Very soft metal with silvery white luster when cut. Ignites in air and reacts violently with water. Finds little use outside research. Minerals with a high Rb content are use for age-dating by the Rb-Sr isotope method. Most minerals containing potassium (K) also contain Rb in trace amounts.

Diagnostic tests: 
In solution, rubidium will give a flame test color of a nice red. This flame test will be contaminated with the colors of the other alkaline elements which are present in the sample (in particular the red color from calcium). You will probably need a diffraction spectroscope to view the red emission lines from rubidium.

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