Actinium (Ac)

Silvery-white, glowing with an eerie blue light;[1] sometimes with a golden cast

Actinium is the namesake of the actinide series, glowing blue in the dark from exciting the air around it, and with [Rn] 6d¹ 7s², actinium-227 (half-life 21.8 years) decays by both alpha and beta emission. Its decay chain produces bismuth-211, which is being researched as a targeted alpha therapy for cancer.

Key metrics

Density10.1g/cm³

Melting point1,323K

Boiling point3,500K

Electronegativity1.1Pauling

Discovery

1899discovered

Discovered by: André-Louis Debierne
Reactivity profile: Strongly radioactive
Reactivity: High
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Rn]}\; \textcolor{#22c55e}{6_{d}^{1}}\; \textcolor{#ef4444}{7_{s}^{2}}

[Rn] 6d1 7s2

Wave function

\Psi_{\text{Ac}} \approx \frac{1}{\sqrt{89!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{89}(\mathbf{r}_{89}) \right|

Probability density $|\Psi|^2$ across the Ac valence shell.

Crystal structure

Face-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number12

Atoms per cell4

Atomic packing factor0.74

Physical properties

Atomic radius: 195 pm
Ionization energy: 499 kJ/mol
Electron affinity: 35 kJ/mol
Crystal structure: Face-centered cubic

Oxidation states

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1323 K3500 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

468.0nmAc I (blue)Blue60%

511.0nmAc I (green)Green100%

530.0nmAc IGreen40%

Dominant line 511.0 nmRange 468–530 nmTransitions 3