Americium (Am)
Actinide · Radioactive · Synthetic
Americium is probably in your home right now: a microscopic speck of Am-241 makes most ionisation smoke detectors work. It was discovered during the Manhattan Project and announced, improbably, on a children's radio quiz show.
Position on the periodic table
Atomic properties
| Atomic number | 95 |
|---|---|
| Atomic mass | 243 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f7 |
| Noble gas shorthand | [Rn] 5f7 7s2 |
| Electrons per shell | 2, 8, 18, 32, 25, 8, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 1.13 |
| Covalent radius (approx.) | 180 pm |
| First ionization energy | 578 kJ/mol |
| Electron affinity | 9.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 12 g/cm³ |
| Melting point | 1175.8 °C (1449 K) |
| Boiling point | 2606.8 °C (2880 K) |
| Appearance | silvery white |
| Radioactive | Yes |
| Origin | Synthetic (lab-made) |
Electron configuration of americium
Americium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f7, usually shortened to [Rn] 5f7 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 25, 8, 2), placing it in period 7 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of americium
- Ionisation smoke detectors
- Industrial thickness gauges
- Neutron sources (with beryllium)
Biological role: None.
Occurrence: Entirely synthetic; made in reactors from plutonium.
Common compounds of americium
AmO2
Americium dioxide
History and discovery
Discovered: 1944 — Glenn T. Seaborg. Name origin: Named after the Americas, parallel to europium.
Seaborg, James, Morgan and Ghiorso synthesised americium in Chicago in 1944.
Safety notes
The speck in a smoke detector is safely sealed; bulk americium is severely radiotoxic.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Americium
1. What is the chemical symbol of Americium?
2. What is the atomic number of Americium?
3. Which category does Americium belong to?
4. What is the state of Americium at room temperature?
5. Which period of the periodic table is Americium in?
Americium FAQs
What is the atomic number of americium?
Americium's atomic number is 95 — every americium atom has 95 protons in its nucleus.
What is the symbol for americium?
Am. Named after the Americas, parallel to europium.
Is americium a metal, nonmetal, or metalloid?
Americium is classified as a actinide.
What state is americium at room temperature?
At about 25 °C, americium is a solid. It melts at 1175.8 °C.
What is americium used for?
Key uses include: ionisation smoke detectors; industrial thickness gauges; neutron sources (with beryllium).
Related elements
Keep working with this element
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