Periodic TableActinium (Ac)
Actinium is an actinide with atomic number 89, in period 7, in the f-block of the periodic table. Its atomic mass is 227 u and its electron configuration is [Rn] 6d¹ 7s². Solid at 25 °C.
Key facts
| Atomic number | 89 |
|---|---|
| Atomic mass | 227 u |
| Category | Actinide |
| Period | 7 |
| Group | f-block, no group number |
| Block | f |
| Electron configuration | [Rn] 6d¹ 7s² |
| Electrons per shell | 2, 8, 18, 32, 18, 9, 2 |
| Electronegativity (Pauling) | 1.1 |
| Oxidation states | +3common in bold |
| State at 25 °C | Solid |
| Melting point | 1323 K1049.85 °C |
| Boiling point | 3473 K3199.85 °C |
| Density | 10.07 g/cm³ |
Atomic properties
| First ionization energy | 5.38 eV |
|---|---|
| Electron affinity | --- |
| Atomic radius | 188 pm |
| Covalent radius | 215 pm |
| Van der Waals radius | 260 pm |
| Common ions | Ac_{4+} |
| Protons, neutrons, electrons | 89, 138, 89 |
Physical and thermal properties
| Molar volume | 22.55 cm³/mol |
|---|---|
| Heat of fusion | 14 kJ/mol |
| Heat of vaporization | 400 kJ/mol |
| Specific heat | 120 J/(kg·K) |
| Thermal conductivity | 12 W/(m·K) |
| Thermal expansion | --- |
| Mohs hardness | --- |
| Young’s modulus | --- |
| Crystal structure | Face-centered cubic |
| Magnetic type | --- |
Identification and history
| CAS number | 7440-34-8 |
|---|---|
| Latin name | Actinium |
| Discovered by | André-Louis Debierne · 1899 |
| Named by | André-Louis Debierne · 1899 |
Natural isotopes
Actinium has no stable isotopes: every isotope is radioactive.
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Actinium in the app
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