Americium (Am)
Actinide · f-block · period 7
Silvery-white radioactive metal that slowly tarnishes in dry air.
Americium (symbol Am) is chemical element number 95, a actinide in the actinide series (f-block), period 7 of the periodic table. Its standard atomic weight is (243) and its electron configuration is [Rn] 5f7 7s2. At room temperature it is a solid, and it is radioactive. Named after the Americas, by analogy with europium above it.
Properties
| Atomic number | 95 |
|---|---|
| Atomic mass | (243) |
| Category | Actinide |
| Block | f-block |
| Group · Period | f-block series · 7 |
| Electron configuration | [Rn] 5f7 7s2 |
| Electrons per shell | 2, 8, 18, 32, 25, 8, 2 |
| State at 25 °C | solid |
| Melting point | 1449 K |
| Boiling point | 2880 K |
| Density | 12 g/cm³ |
| Electronegativity (Pauling) | 1.13 |
| Radioactive | Yes — no stable isotope |
| Origin | synthetic |
| Discovered | 1944 · Seaborg, James, Morgan & Ghiorso |
Key facts about Americium
- Named after the Americas, by analogy with europium above it.
- A tiny speck of americium sits in almost every household smoke detector.
- Its alpha particles ionise the air in the detector; smoke breaks the current and sets off the alarm.
- First made in a reactor during the Manhattan Project.
What Americium is used for
Ionisation smoke detectors, industrial thickness and density gauges, portable X-ray and neutron sources.
Where it sits in the periodic table
Americium is in the actinide series, period 7, of the f-block. Its electron configuration [Rn] 5f7 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Americium on the interactive table →
Americium — frequently asked questions
What is Americium used for?
Ionisation smoke detectors, industrial thickness and density gauges, portable X-ray and neutron sources.
Is Americium radioactive?
Yes. Americium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Americium?
Americium has the electron configuration [Rn] 5f7 7s2, which is 2, 8, 18, 32, 25, 8, 2 electrons per shell.
What group and period is Americium in?
Americium is in the actinide series (f-block), period 7, in the f-block. Its outer shell holds 2 electrons.
Who discovered Americium?
Americium was discovered in 1944 by Seaborg, James, Morgan & Ghiorso.