Actinides
Americium
A synthetic metal used in household smoke detectors.
Atomic #95Mass[243]Blockf-blockPeriod7Group—
Am95 · [243]
3D Atom Explorer
Inside the Americium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Americium atom step by step.
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Electron configuration
[Rn] 5f7 7s2
A neutral Americium atom has 95 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Shell 12 e⁻Shell 28 e⁻Shell 318 e⁻Shell 432 e⁻Shell 525 e⁻Shell 68 e⁻Shell 72 e⁻
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Properties
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 1449 K (1176 °C)
- Boiling point
- 2880 K (2607 °C)
- Density
- 13.69 g/cm³
- Electronegativity
- 1.13 Pauling
- Atomic radius
- 175 pm
- 1st ionization energy
- 578 kJ/mol
- Category
- Actinides
History
Discovery & naming
- Discovered
- 1944
- Discovered by
- Glenn Seaborg and colleagues
- Origin of name
- The Americas.
Notable uses
Ionization smoke detectors.
Cosmic origin
Where Americium comes from
Human synthesis
Made in reactors by loading plutonium with neutrons. A speck of it sits in many smoke detectors.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 95
- Atomic mass
- [243]
- Category
- Actinides
- Group · Period
- — · 7
- Block
- f-block
- Shells
- 2 · 8 · 18 · 32 · 25 · 8 · 2