Name lanthanum
Symbol La
Atomic Weight 138.9055
Atomic Number 57
CAS ID 7439-91-0
Group Number
Group Name Lanthanoid
Period Number 6
Origin of Name From the Greek, lanthanein = "to lie hidden."
Year Discovered 1839
Discovery Credits Discovered by C. G. Mosander at Stockholm, Sweden.
Class Metallic
Color Silvery White
Standard State Solid at 77 F & 298 K
Description Soft, silvery-white metal; rapidly tarnishes in air and burns easily. Reacts with water to give hydrogen gas. Used in optical glass and for flints. La2+ is used as a biological tracer for calcium Ca2+.

Diagnostic tests: 
There are no simple diagnostic tests to identify lanthanum.
X-ray fluorescence spectroscopy is commonly employed to identify and analyze members of the Rare-Earth group elements.

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