89 · Ac
Actinium
Reported by Debierne in 1899. Giesel finds it independently in 1902 under the name emanium.
Identity
- Atomic number
- 89
- Symbol
- Ac
- Canonical name
- Actinium
- Category
- actinide
- Group
- unassigned
- Period
- 7
- Block
- f
Series set apart from the main table. Whether group 3 is lanthanum or lutetium (actinium or lawrencium) is still discussed, so the group is left empty.
Properties
These quantities come from the Periodic Table JSON compilation. They have not yet been checked, one by one, against CIAAW atomic weights or NIST measurements. A value marked estimated is not a measurement.
- Atomic mass
- [227] No standard atomic weight. The number shown is the conventional mass number used in tables, not a measured mass in u.
- Electron configuration
- [Rn] 6d1 7s2
- Electrons per shell
- 2, 8, 18, 32, 18, 9, 2
- Standard state
- solid
- Density
- 10 g/cm³
- Melting point
- 1,500 K
- Boiling point
- 3,500 K
- Electronegativity
- 1.1 Pauling
- First ionization energy
- 499 kJ/mol
- Electron affinity
- 33.77 kJ/mol
Notable isotopes
This summary is not an inventory of every isotope.
Conventional mass number: 227
History
Actinium
Discovery · confirmed · 1899
Debierne reports actinium in pitchblende residues.
Emanium
Discovery · claimed · 1902
Giesel independently finds a substance he calls emanium. It is later identified with actinium.
Etymology
- Theme
- property
- Language
- grec
- Root
- aktis
- Meaning
- ray
Scientists
Places and institutions
- Paris — historical setting : France — present country : France
Sources
- IUPAC, Periodic Table of the Elements
- Bowserinator, Periodic Table JSON. Compilation secondaire d’où viennent les grandeurs physiques importées (masse, densité, températures, énergies). Elles ne sont pas revérifiées une à une auprès du NIST ou de la CIAAW.
- John Emsley, Nature’s Building Blocks: An A–Z Guide to the Elements