Ac
Actinium
Element 89 · Actinide
Actinium (Ac)
Actinium is a soft, radioactive metal that glows pale blue in the dark. It gives its name to the actinide series.
- Actinide
- Period 7
- f-block series
- f-block
- solid at room temperature
- ☢ Radioactive
Key properties
- Atomic mass
- [227]
- u
- Electron configuration
- [Rn] 6d1 7s2
- Melting point
- 1,050.9 °C
- 1,324 K
- Boiling point
- 3,197.9 °C
- 3,471 K
- Density
- 10.07 g/cm³
- Electronegativity
- 1.1
- Pauling
- Atomic radius
- 260 pm
- van der Waals
- 1st ionisation energy
- 5.17 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about actinium
- 01
Friedrich Oskar Giesel independently discovered it in 1902.
- 02
It is about 150 times more radioactive than radium.
- 03
Actinium-225 is a promising isotope for targeted alpha therapy.
Applications
What is actinium used for?
- Targeted cancer therapy research
- Neutron sources
History
Discovery & name origin
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 89
- Atomic mass
- [227] u
- Group
- Actinides (3)
- Period
- 7
- Block
- f-block
- Electron configuration
- [Rn] 6d1 7s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d1
- Electrons per shell
- 2, 8, 18, 32, 18, 9, 2
- Electronegativity (Pauling)
- 1.1
- Electron affinity
- —
- Atomic radius (van der Waals)
- 260 pm
- Stable isotopes
- None — all isotopes are radioactive
Oxidation states
Highlighted: common oxidation states (+3).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st499
- 2nd1,170
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 1,324 K · 1,050.9 °C · 1,923.5 °F
- Boiling point
- 3,471 K · 3,197.9 °C · 5,788.1 °F
- Density
- 10.07 g/cm³
- Molar heat capacity
- 27.2 J/(mol·K)
- Appearance
- —
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Actinium questions
What is Ac on the periodic table?
Ac is the symbol for actinium, element 89 on the periodic table. It sits in period 7, in the f-block, in the actinide category, and has an atomic mass of [227].
What is the atomic number of actinium?
Actinium has atomic number 89, so every actinium atom has 89 protons in its nucleus. Its symbol is Ac and its atomic mass is [227].
Who discovered actinium?
Actinium was discovered by André-Louis Debierne in 1899 (France). The name comes from Greek aktinos, “ray”.
What is actinium used for?
Actinium is used for: targeted cancer therapy research; neutron sources.
Is actinium a metal?
Yes. Actinium is a actinide, one of the metallic elements.
What is the electron configuration of actinium?
The electron configuration of actinium is [Rn] 6d1 7s2. Its 89 electrons are arranged in shells as 2, 8, 18, 32, 18, 9, 2.