89227AcActinium
Actinium (Ac) — element 89actinide · period 7
Actinium is a chemical element with the symbol Ac and atomic number 89. It is an actinide in period 7 of the periodic table (the f-block), with a standard atomic mass of 227 u. At room temperature (25 °C) actinium is a solid.
💡 Known for: Glows pale blue in the dark because of its intense radioactivity; actinium-225 is used in cancer therapy.
# Actinium properties
| Symbol | Ac |
|---|---|
| Atomic number | 89 |
| Atomic mass | 227 u |
| Category | actinide |
| Group | — (f-block, no group number) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 6d¹ 7s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s² |
| Electrons per shell | 2, 8, 18, 32, 18, 9, 2 |
| Protons / electrons | 89 / 89 |
| State at 25 °C | solid |
| Melting point | 1323 K (1049.8 °C, 1921.7 °F) |
| Boiling point | 3471 K (3197.8 °C, 5788.1 °F) |
| Density | 10.07 g/cm³ |
| Electronegativity (Pauling) | 1.1 |
| First ionization energy | 5.17 eV |
| Atomic radius | 195 pm |
| Discovered | 1899 |
# Electron configuration of actinium
The electron configuration of actinium is [Rn] 6d¹ 7s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s². Its 89 electrons fill 7 shells as 2, 8, 18, 32, 18, 9, 2, so the outermost shell holds 2 electrons.
# Related elements
RaRadiumprevious elementThThoriumnext elementPaProtactiniumactinideUUraniumactinideNpNeptuniumactinidePuPlutoniumactinideAmAmericiumactinideCmCuriumactinideBkBerkeliumactinideCfCaliforniumactinide
# Actinium FAQ
What is the atomic number of actinium?
The atomic number of actinium is 89: every actinium atom has 89 protons in its nucleus. Its symbol is Ac.
What is the atomic mass of actinium?
The standard atomic mass of actinium is 227 u.
What is the electron configuration of actinium?
Actinium's electron configuration is [Rn] 6d¹ 7s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s²), with 2, 8, 18, 32, 18, 9, 2 electrons per shell.
Is actinium a metal?
Yes. Actinium is an actinide, one of the metals.
What is the melting point of actinium?
Actinium melts at 1323 K (1049.8 °C, 1921.7 °F) and boils at 3471 K (3197.8 °C, 5788.1 °F).
What is actinium used for / known for?
Glows pale blue in the dark because of its intense radioactivity; actinium-225 is used in cancer therapy.