Actinium (Ac)
Actinium (Ac) is element 89 of the periodic table, an actinide in period 7, in the f-block. It has no stable isotope and no standard atomic weight; 227 is the mass number of its longest-lived isotope. At room temperature it is a solid; it melts at 1050.85 °C and boils at 3197.85 °C.
| Atomic number | 89 |
|---|---|
| Symbol | Ac |
| Standard atomic weight | [227] (mass number of the longest-lived isotope) |
| Molar mass | [227] g/mol |
| Category | Actinide |
| Group | f-block (actinide series) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 7s2 6d1 |
| Oxidation states | +3 |
| Electronegativity (Pauling) | 1.1 |
| Atomic radius (van der Waals) | 260 pm |
| First ionisation energy | 5.17 eV (498.8 kJ/mol) |
| Electron affinity | — |
| State at room temperature | Solid |
| Melting point | 1324 K (1050.85 °C) |
| Boiling point | 3471 K (3197.85 °C) |
| Density | 10.07 g/cm³ |
| Discovered | 1899 |
Actinides
Th · ThoriumPa · ProtactiniumU · UraniumNp · NeptuniumPu · PlutoniumAm · AmericiumCm · CuriumBk · BerkeliumCf · CaliforniumEs · EinsteiniumFm · FermiumMd · MendeleviumNo · Nobelium
Calculate with Actinium
Atomic weight: IUPAC CIAAW — no standard atomic weight; mass number in brackets. Other properties: PubChem (U.S. National Library of Medicine, public domain). Values such as melting point and radius depend on how they were measured; check a data book for precise work.