---
title: "Americium (Am) — element 95"
description: "Americium is element 95, symbol Am, most stable isotope 243. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/americium/
site: "At One Place"
---

# Americium (Am)

**Americium — element 95: Am**

[243] · Actinide · period 7

There is a synthetic element in most people's hallway: an ionisation smoke detector contains about 0.3 micrograms of americium-241, whose alpha particles ionise the air in a small chamber so that smoke entering it changes the current. Seaborg and his group announced americium and curium in November 1945 not in a journal but on a children's radio quiz show, five days before the formal presentation, after a young panellist asked whether any new elements had been discovered. Americium-241 is also the strongest common source of low-energy gamma rays used for calibration.

## Properties

- **Atomic number:** 95
- **Symbol:** Am
- **Mass number of most stable isotope:** [243]
- **Category:** Actinide
- **Period:** 7
- **Block:** f-block
- **Electron configuration:** [Rn] 7s² 5f⁷
- **Electrons per shell:** 2, 8, 18, 32, 25, 8, 2
- **Melting point:** 1,449 K — 1175.8 °C — 2148.5 °F
- **Boiling point:** 2,284 K — 2010.8 °C — 3651.5 °F
- **Density:** 13.69 g/cm³
- **Electronegativity:** 1.3 (Pauling)
- **Oxidation states:** +3, +4, +5, +6
- **Discovered:** 1944 by Glenn Seaborg, Ralph James, Leon Morgan and Albert Ghiorso

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁷
- **Noble gas shorthand:** [Rn] 7s² 5f⁷
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 25 · P: 8 · Q: 2

## What it is used for

- Ionisation smoke detectors — the commonest consumer use of any synthetic element
- Thickness and density gauges in paper and steel mills
- Well-logging neutron sources in oil exploration
- Proposed long-life power source for European deep-space missions

## Hazards

- Alpha emitter with a 432-year half-life; dangerous if the source is broken open and inhaled
- Intact smoke detectors are safe — the source is sealed in a metal foil

> No stable isotope; the mass given is the mass number of americium-243, the longest-lived at 7,370 years. The smoke detector isotope is americium-241, half-life 432 years.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 93 | Neptunium | Np | [237] |
| 94 | Plutonium | Pu | [244] |
| 95 | Americium ← | Am | [243] |
| 96 | Curium | Cm | [247] |
| 97 | Berkelium | Bk | [247] |

## Common questions

### What is the atomic number of americium?

95. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for americium?

Am.

### What is the electron configuration of americium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁷, or [Rn] 7s² 5f⁷ in noble-gas shorthand.

### What is the melting point of americium?

1,449 K — 1175.8 °C — 2148.5 °F

## Related pages

- [Neptunium (Np)](https://atoneplace.net/element/neptunium/)
- [Plutonium (Pu)](https://atoneplace.net/element/plutonium/)
- [Curium (Cm)](https://atoneplace.net/element/curium/)
- [Berkelium (Bk)](https://atoneplace.net/element/berkelium/)

## Sources

- Official vendor product documentation — At One Place (/about/)