Element 89
Actinium
Actinides
Actinium (Ac) is in the f-block of the periodic table — group 3, period 7.
Actinium is a radioactive chemical element with symbol Ac (not to be confused with the abbreviation for an acetyl group) and atomic number 89, which was discovered in 1899.
Key data
- Atomic number
- 89
- Atomic mass
- 227.000 u
- Group / Period
- 3 / 7
- Block
- f-block
- Phase at STP
- Solid
- Density
- 10 g/cm³
- Melting point
- 1226.8 °C
- Boiling point
- 3226.8 °C
- Electron configuration
- [Rn] 6d1 7s2
Periodic table block
Actinium is in the f-block (group 3, period 7). Elements land in the f-block when their highest-energy electrons fill an f subshell — these are the lanthanides and actinides shown beneath the main table.
New to this? Periodic table blocks explained: s, p, d, and f
Common uses
- •Targeted alpha cancer therapy
- •Neutron sources
- •Radioactive
Discovery
Year: 1899
Discovered by: Friedrich Oskar Giesel
Frequently asked questions
What is the atomic number of Actinium?
Actinium has atomic number 89. Its symbol is Ac and its atomic mass is 227 u.
What category of element is Actinium?
Actinium is classified as actinides. It sits in group 3, period 7 of the periodic table.
What block of the periodic table is Actinium in?
Actinium is in the f-block (group 3, period 7). Its highest-energy electrons occupy the f subshell — you can see this in its electron configuration, [Rn] 6d1 7s2.
What is Actinium used for?
Common uses of Actinium include: Targeted alpha cancer therapy, Neutron sources, Radioactive.
When was Actinium discovered?
Actinium was discovered in 1899 by Friedrich Oskar Giesel.
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