Name Actinium
Symbol Ac
Atomic Number 89
Atomic Mass 227.0 atomic mass units
Number of Protons 89
Number of Neutrons 138
Number of Electrons 89
Melting Point 1050.0° C
Boiling Point 3200.0° C
Density 10.07 grams per cubic centimeter
Normal Phase Solid
Family Rare Earth Metals
Period 7
Cost Unavailable



Origin of Name From the Greek aktinos, meaning ray
Date and Place of Discovery In 1899 in France and again in 1902 in France
Discovered by André-Louis Debierne (1899) and
F. Giesel (1902)
Common Compounds No known compounds
Interesting facts
  • It is extremely rare.
  • It was discovered in pitchblende residues after radium was extracted.
  • It is found in traces of uranium ore.
  • Its high radioactivity creates a glowing pale blue light.
  • It is about 150 times more radioactive than radium.
  • Its chemical behavior similar to lanthanum.
Common Uses
There are no significant applications outside the laboratory.


Photo Courtesy of
Chemical Elements
Jefferson Lab
Mrs. Purdy's Web Page
Web Elements

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