About

Actinium is a soft, silvery-white radioactive metal that gives its name to the actinide series. It is about 150 times as radioactive as radium, glowing with a pale blue light in the dark due to its intense radioactivity. This property makes it a valuable neutron source for research, but it has few other industrial uses. It is found in trace amounts in uranium ore.

Atomic Properties

Atomic Number89

Atomic Weight227 u

Neutrons (common)138

Electron Configuration[Rn] 6d¹ 7s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s²

Electrons per Shell2, 8, 18, 32, 18, 9, 2

Electronegativity1.1

Electron Affinity33.77 kJ/mol

Oxidation States+3

Covalent Radius200 pm

Ionic Radius112.6 pm

Periodic Table Position

Group3

Period7

BlockD

Chemical SeriesActinoids

Physical Properties

State at STPsolid

Appearancesilvery-white radioactive metal

Crystal Structurefcc

Magnetic Orderingparamagnetic

Thermal Properties

Melting Point1,323 K

Boiling Point3,471 K

Thermal Conductivity12 W/(m·K)

Specific Heat0.12 J/(g·K)

Molar Heat27.24 J/(mol·K)

Heat of Fusion14 kJ/mol

Heat of Vaporization400 kJ/mol

Abundance

In Earth's Crust0 ppm

Discovery

Discovered byAndré-Louis Debierne

Discovery Year1,899

Occurrencefrom_decay

CAS Number7440-34-8

Electron Configuration

Energy

↿⇂

1s

↿⇂

2s

↿⇂

2p

↿⇂

3s

↿⇂

3p

↿⇂

4s

↿⇂

3d

↿⇂

4p

↿⇂

5s

↿⇂

4d

↿⇂

5p

↿⇂

6s

↿⇂

4f

↿⇂

5d

↿⇂

6p

↿⇂

7s

5f

↿

6d

7p

Isotopes of Actinium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²²⁷Ac	227.027750	Trace	21.772 y	Beta Minus Decay, Alpha Decay