Americium (Am)

Silvery metal

Americium is the only actinide found in households—in the ionization chamber of every smoke detector, and with a half-filled 5f⁷ shell, americium-241 (half-life 432 years) emits alpha particles that ionize air. When smoke disrupts the ion current, the alarm triggers. About 100,000 Ci are used annually in smoke detectors worldwide.

Key metrics

Density13.7g/cm³

Melting point1,449K

Boiling point2,880K

Electronegativity1.3Pauling

Discovery

1944discovered

Discovered by: Glenn T. Seaborg
Reactivity profile: Radioactive
Reactivity: Medium
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Rn]}\; \textcolor{#a855f7}{5_{f}^{7}}\; \textcolor{#ef4444}{7_{s}^{2}}

[Rn] 5f7 7s2

Wave function

\Psi_{\text{Am}} \approx \frac{1}{\sqrt{95!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{95}(\mathbf{r}_{95}) \right|

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

Crystal structure

Double Hexagonal Close-Packed

Lattice constantsa 1.00 · b 1.00 · c 2.00

Cell anglesα 90° · β 90° · γ 120°

Coordination number12

Atoms per cell4

Atomic packing factor0.74

Physical properties

Atomic radius: 173 pm
Ionization energy: 578 kJ/mol
Electron affinity: 0 kJ/mol
Crystal structure: Double hexagonal close-packed

Oxidation states

+2+3+4+5+6

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1449 K2880 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

455.0nmAm I (blue)Blue100%

488.0nmAm IBlue40%

525.0nmAm I (green)Green60%

Dominant line 455.0 nmRange 455–525 nmTransitions 3