Actinium (Ac) – element 89
Actinium is a chemical element with the symbol Ac and atomic number 89. It is a actinide in group 3 (actinides), period 7 of the periodic table (f-block), and is a solid at room temperature.
Actinium (Ac) has atomic number 89, atomic mass [227] and electron configuration [Rn] 6d1 7s2.
Actinium facts
| Symbol | Ac |
|---|---|
| Atomic number | 89 |
| Atomic mass | [227] |
| Category | actinide |
| Group | group 3 (actinides) |
| Period | 7 |
| Block | f-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d1 |
| Noble-gas notation | [Rn] 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 9, 2 |
Bohr model and shells
Actinium has 89 electrons in 7 shells: 2, 8, 18, 32, 18, 9, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 1500 K (1226.8 °C) |
|---|---|
| Boiling point | 3500 K (3226.8 °C) |
| Density | 10 g/cm³ |
| Electronegativity (Pauling) | 1.1 |
| Electron affinity | 33.77 kJ/mol |
| Ionization energies | 499, 1170 kJ/mol (1st, 2nd) |
| Molar heat capacity | 27.2 J/(mol·K) |
| Discovered by | Friedrich Oskar Giesel |
Use the atomic mass in the molar mass calculator for any formula containing Ac.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of actinium?
The atomic mass of actinium is [227] (mass number of its longest-lived isotope, since it has no stable isotope).
What is the electron configuration of actinium?
Actinium has 89 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d¹, or [Rn] 6d¹ 7s² in noble-gas notation. Electrons per shell: 2, 8, 18, 32, 18, 9, 2.
Is actinium a metal?
Yes. Actinium is a actinide.
Where is actinium on the periodic table?
Actinium is in group 3 (actinides), period 7, in the f-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.