Actinium
Silvery radioactive metallic element, belongs to group 3 of the periodic table. The most stable isotope, Ac-227, has a half-life of 217 years. Ac-228 (half-life of 6.13 hours) also occurs in nature. There are 22 other artificial isotopes, all radioactive and having very short half-lives. Chemistry similar to lanthanumpy. Used as a source of alpha particles. Discovered by A. Debierne in 1899.
Gallery
Oak Ridge National Laboratory, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons, source: https://www.flickr.com/photos/oakridgelab/31481701837/
Physical Propertiesmass · density · phase · crystal
Atomic Mass
227Da
Density
10g/cm³
Phase (STP)
Solid
Melting Point
1323.2K
Boiling Point
3473.2K
Molar Heat
0.1200J/(mol·K)
Crystal Structure
FCC
Lattice Constant
5.310Å
Atomic Radiiatomic · covalent · van der Waals
Atomic (Empirical)
195.00pm
Covalent
186.00pm
Van der Waals
247.00pm
Electronic Propertieselectronegativity · ionization · affinity
Electron Configuration
[Rn] 6d 7s2
Electron Shells
2, 8, 18, 32, 18, 9, 2
Electronegativity
1.10Pauling
Electron Affinity
0.3kJ/mol
1st Ionization Energy
5.4kJ/mol
Oxidation States
+3
Orbital DiagramAufbau · Hund's rule · Pauli exclusion
Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2Short: [Rn] 6d 7s2
Ionization Energies (89 known)
Emission Spectrumvisible range · characteristic spectral lines
Abundanceby mass
Log scale · ppm = parts per million by mass
Biological Role
Radioactive. Ac-225 studied for targeted alpha therapy against cancer.
Discovery
Discovered By
André Debierne
Named By
—
Year
1899
Nuclear Data
Known Isotopes
33
Stable Isotopes
0
Stable Mass Numbers
None