(From the Greek aktinos, "ray") A white, radioactive, metallic chemical element, the first member of the actinide series, found in pitchblende and other minerals or formed in reactors by the neutron irradiation of radium.

Symbol: Ac
Atomic number: 89
Atomic weight: 227 (isotope with the longest known half-life)
Density (at room temperature and pressure): 10.07 g/cc
Melting point: 1,050°C
Boiling point: 3,200°C
Ground state electron configuration: [Rn]6d17s2


Symbol: Ac
Atomic number: 89
Average atomic weight: special
Valencies: 3
Electronic configuration: [Rn] 6d1 7s2
Melting point: 1050°C ( 1323°K)
Boiling point: 3200°C ( 3473°K)
Heat of fusion: ? kJ/mol
Heat of vaporization: ? kJ/mol
Specific heat: ? J/gK
Physical state at STP: liquid?
Natural abundance: 3 * 10-15
Absolute abundance: ?
Density: 10.07 g/cm3
Electronegativity: 1.1
Ionization Potential: 5.17 V
Crystallisation: Face centered cubic
Discovered by: Andre Debierne
Discovery date: 1899
Name origin: From actinos, Greek word meaning ray
Group: 3 (Rare Earth)

This silvery metal has no known stable isotopes. The most stable isotope is 227Ac, with a half life of 21.773 years.

Spectral lines:

none listed

Alternate spellings:

French: same as English
German: same as English

Isotopes of Actinium

Stable isotopes: none

Isotopes with a half-life of more than one million years: none

Isotopes with a half-life of more than one year:

Isotopes with a half-life of more than one hour:

Isotopes with a half-life of more than one second:

Isotopes with a half-life of less than one second:

Ac*tin"i*um (#), n. [Gr. , , ray.] Chem.

A supposed metal, said by Phipson to be contained in commercial zinc; -- so called because certain of its compounds are darkened by exposure to light.


© Webster 1913.

Editor's note: 'Phipson' appears to be Thomas Lamb Phipson, a London scientist of the late 1800's. His surmise appears to have been mistaken, and today's actinium 89 is not related to zinc.

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