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95Am[243]
Actinidessolid at STPF-block

Americium

Group: f-block•Period: 7•Standard Atomic Weight: [243] u
Open Full Periodic TableView Bohr Model

Why is Americium in this position?

Understanding the scientific rationale behind Americium's position in the periodic table:

Group Assignment
Group Lanthanide / Actinide

Actinide series element filling the 5f subshell.

Period Assignment
Period 7

Belongs to Period 7 because its outermost electrons occupy n=7.

Orbital Block
F-block

Belongs to the f-block because its 5f subshell is exactly half-filled (5f⁷ 7s²).

Chemical Category
Actinides

Classified as an actinide radioactive metal.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 32, 25, 8, 2]

Bohr Atomic Shell Model(2, 8, 18, 32, 25, 8, 2)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

95 Protons (p⁺)148 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 18Shell M: Electron 2 of 18Shell M: Electron 3 of 18Shell M: Electron 4 of 18Shell M: Electron 5 of 18Shell M: Electron 6 of 18Shell M: Electron 7 of 18Shell M: Electron 8 of 18Shell M: Electron 9 of 18Shell M: Electron 10 of 18Shell M: Electron 11 of 18Shell M: Electron 12 of 18Shell M: Electron 13 of 18Shell M: Electron 14 of 18Shell M: Electron 15 of 18Shell M: Electron 16 of 18Shell M: Electron 17 of 18Shell M: Electron 18 of 18NShell N: Electron 1 of 32Shell N: Electron 2 of 32Shell N: Electron 3 of 32Shell N: Electron 4 of 32Shell N: Electron 5 of 32Shell N: Electron 6 of 32Shell N: Electron 7 of 32Shell N: Electron 8 of 32Shell N: Electron 9 of 32Shell N: Electron 10 of 32Shell N: Electron 11 of 32Shell N: Electron 12 of 32Shell N: Electron 13 of 32Shell N: Electron 14 of 32Shell N: Electron 15 of 32Shell N: Electron 16 of 32Shell N: Electron 17 of 32Shell N: Electron 18 of 32Shell N: Electron 19 of 32Shell N: Electron 20 of 32Shell N: Electron 21 of 32Shell N: Electron 22 of 32Shell N: Electron 23 of 32Shell N: Electron 24 of 32Shell N: Electron 25 of 32Shell N: Electron 26 of 32Shell N: Electron 27 of 32Shell N: Electron 28 of 32Shell N: Electron 29 of 32Shell N: Electron 30 of 32Shell N: Electron 31 of 32Shell N: Electron 32 of 32OShell O: Electron 1 of 25Shell O: Electron 2 of 25Shell O: Electron 3 of 25Shell O: Electron 4 of 25Shell O: Electron 5 of 25Shell O: Electron 6 of 25Shell O: Electron 7 of 25Shell O: Electron 8 of 25Shell O: Electron 9 of 25Shell O: Electron 10 of 25Shell O: Electron 11 of 25Shell O: Electron 12 of 25Shell O: Electron 13 of 25Shell O: Electron 14 of 25Shell O: Electron 15 of 25Shell O: Electron 16 of 25Shell O: Electron 17 of 25Shell O: Electron 18 of 25Shell O: Electron 19 of 25Shell O: Electron 20 of 25Shell O: Electron 21 of 25Shell O: Electron 22 of 25Shell O: Electron 23 of 25Shell O: Electron 24 of 25Shell O: Electron 25 of 25PShell P: Electron 1 of 8Shell P: Electron 2 of 8Shell P: Electron 3 of 8Shell P: Electron 4 of 8Shell P: Electron 5 of 8Shell P: Electron 6 of 8Shell P: Electron 7 of 8Shell P: Electron 8 of 8QShell Q: Electron 1 of 2Shell Q: Electron 2 of 2AmZ = 95

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):18 / 18 electrons (100%)
Shell N (n=4):32 / 32 electrons (100%)
Shell O (n=5):25 / 50 electrons (50%)
Shell P (n=6):8 / 72 electrons (11%)
Shell Q (n=7):2 / 98 electrons (2%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁷ 6s² 6p⁶ 7s²

Neutral ground state configuration. Valence electrons: 9.

Atomic & Quantum Properties

Electronegativity (Pauling)1.3 Pauling
1st Ionization Energy578 kJ/mol
Electron Affinity-48 kJ/mol
Atomic Radius (empirical)180 pm
Common Oxidation States+3
Crystal StructureDouble HCP

Physical & Thermal Properties

Density at STP12.0 g/cm³
Melting Point1176 °C (1449 K)
Boiling Point2607 °C (2880 K)
Magnetic OrderingParamagnetic
Discovery Year1944
Discovered ByGlenn T. Seaborg, Ralph A. James, Leon O. Morgan & Albert Ghiorso

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Household ionization smoke detectors (Americium-241 alpha particles ionize air chamber to sense smoke particles)
  • Industrial fluid density and sheet metal thickness gauging
  • Portable neutron sources for oil well logging and mineral prospecting (Am-Be sources)
  • Deep space radioisotope power supplies under development by the European Space Agency
Occurrence in Nature

Synthesized commercially in nuclear power reactors by successive neutron capture on Plutonium-239.

Etymology & Name Origin

Named after the Americas, by analogy with its lanthanide homologue Europium (Europe)

Important Chemical Compounds
AmO₂ (Americium dioxide)
AmCl₃ (Americium trichloride)
Interesting Chemical Facts
  • • Americium is the only synthetic, man-made chemical element that ordinary consumers can buy over the counter at a hardware store (inside smoke detectors).
  • • Americium was synthesized during the secret World War II Manhattan Project in 1944 and humorously revealed by Seaborg on a children's radio quiz show.
  • • Americium-241 in a household smoke detector contains roughly 0.29 micrograms of americium, delivering virtually zero external radiation dose to occupants.
Safety & Handling Note

Radioactive alpha emitter and gamma emitter; sealed securely inside smoke detector ionization chambers.

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