Ac
Actinium
Atomic number: 89Mass: 227 uCategory: Actinide
About Actinium
Actinium is a radioactive element that occurs in nature as an extremely rare trace element in uranium ore. Pure actinium glows blue in the dark due to its intense radioactivity causing air molecules to luminesce. It is the first actinide element.
Properties
Period
7
Group
N/A
Block
F
Category
Actinide
Electronegativity
1.10 (Pauling)
Ionization Energy
499 kJ/mol
Melting Point
1323 K (1050°C)
Boiling Point
3471 K (3198°C)
Density
10 g/cm³
Oxidation States
+3
Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s²
[Rn] 6d¹ 7s²
Shell 1:2e⁻
Shell 2:8e⁻
Shell 3:18e⁻
Shell 4:32e⁻
Shell 5:18e⁻
Shell 6:9e⁻
Shell 7:2e⁻
Real-World Uses
Cancer treatment (Ac-225)
Neutron sources
Research
Nuclear batteries (experimental)
Radioactive tracers
Fun Fact
Actinium glows a ghostly blue in the dark — not because it's coloured, but because its radioactivity causes surrounding air molecules to emit light!