Actinium (Ac)
Actinide · f-block · period 7
Soft, silvery-white metal that glows pale blue in the dark.
Actinium (symbol Ac) is chemical element number 89, a actinide in the actinide series (f-block), period 7 of the periodic table. Its standard atomic weight is (227) and its electron configuration is [Rn] 6d1 7s2. At room temperature it is a solid, and it is radioactive. Its name is Greek for 'ray' — it gives the actinide series its name.
Properties
| Atomic number | 89 |
|---|---|
| Atomic mass | (227) |
| Category | Actinide |
| Block | f-block |
| Group · Period | f-block series · 7 |
| Electron configuration | [Rn] 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 9, 2 |
| State at 25 °C | solid |
| Melting point | 1500 K |
| Boiling point | 3500 K |
| Density | 10 g/cm³ |
| Electronegativity (Pauling) | 1.1 |
| Radioactive | Yes — no stable isotope |
| Origin | decay |
| Discovered | 1899 · André-Louis Debierne |
Key facts about Actinium
- Its name is Greek for 'ray' — it gives the actinide series its name.
- About 150 times more radioactive than radium.
- Glows in the dark from the air it ionises around itself.
- Actinium-225 is a promising source of alpha particles for targeted cancer therapy.
What Actinium is used for
Targeted alpha cancer therapy (research), neutron sources for well-logging and research.
Where it sits in the periodic table
Actinium is in the actinide series, period 7, of the f-block. Its electron configuration [Rn] 6d1 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Actinium on the interactive table →
Actinium — frequently asked questions
What is Actinium used for?
Targeted alpha cancer therapy (research), neutron sources for well-logging and research.
Is Actinium radioactive?
Yes. Actinium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Actinium?
Actinium has the electron configuration [Rn] 6d1 7s2, which is 2, 8, 18, 32, 18, 9, 2 electrons per shell.
What group and period is Actinium in?
Actinium is in the actinide series (f-block), period 7, in the f-block. Its outer shell holds 2 electrons.
Who discovered Actinium?
Actinium was discovered in 1899 by André-Louis Debierne.