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95AmAmericium[243]

Actinide

Americium (Am)

“The only synthetic element you probably own — a whisper of americium lives inside the smoke detector on your ceiling.”

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Atomic number95

Atomic mass[243]

Groupf-block

Period7

BlockF-block

PhaseSolid

Electron structure

How its electrons are arranged

[Rn] 5f⁷ 7s²

Shell 1

2e⁻

Shell 2

8e⁻

Shell 3

18e⁻

Shell 4

32e⁻

Shell 5

25e⁻

Shell 6

8e⁻

Shell 7

2e⁻

Computed from the aufbau principle, with known real-world exceptions applied automatically.

🎯 Exam focus

Questions to practise

Write your answer first, then check it against the notes above.

1How did Seaborg’s Chicago team create americium in 1944 — which element was the neutron target, and what decay turned the product into element 95?

Build your answer from the electron structure, position and properties above — then compare it with the notes.

2Describe how a speck of Am-241 inside an ionization smoke detector turns drifting smoke into an alarm signal.

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3Why can a student honestly claim that a synthetic element sits at home — and which common device makes it possible?

Build your answer from the electron structure, position and properties above — then compare it with the notes.

4Am-241 has a half-life of 432 years and emits alpha particles — explain why these two facts suit it so well for household detectors.

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5Americium’s electron configuration is [Rn] 5f⁷ 7s² — state its period and block, count its f-electrons, and locate it in the actinide row.

Build your answer from the electron structure, position and properties above — then compare it with the notes.

6The naming of americium follows a geographical pattern borrowed from the element sitting just above it — identify that element and explain the symmetry.

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The notes

About the element

Characteristics

Every atom is radioactive: the workhorse isotope Am-241, half-life 432 years, hurls out alpha particles as it decays towards neptunium-237.
Bred inside nuclear reactors from plutonium in gram-scale batches — far more accessible than every heavier synthetic element.
Chemistry is dominated by the +3 oxidation state, but +2, +4, +5 and +6 are all known — a surprisingly rich menu even for an actinide.
Its steady, long-lived alpha decay keeps it dependable for decades: a smoke-detector source made in the 1990s still works faithfully today.

Appearance

A silvery-white, quite hard radioactive metal that slowly tarnishes in air. World production is measured in grams, yet gram-for-gram americium is the most widely distributed synthetic element on Earth, hiding inside smoke detectors in millions of homes and offices.

Real world

Where you meet it

✦ Uses

Ionization smoke detectors: a speck of Am-241 (about a third of a microgram, sealed in gold foil) ionizes the air, and smoke stealing those ions triggers the alarm — hundreds of millions protect homes and offices worldwide.
Am-Be neutron sources: americium paired with beryllium spits out neutrons, serving well-logging probes, industrial gauges and laboratory neutron activation analysis.
A target material for building heavier elements: bombarding americium-243 with ions is one route to berkelium, californium and beyond in research reactors.
Studied as a compact radioisotope power source for spacecraft, since its alpha decay runs warm — though Pu-238 remains the flight favourite.

◍ Everyday examples

The small disc inside the smoke detector on a Bangladeshi school corridor’s ceiling is probably the closest you will ever come to a synthetic element.
Fire-safety rules in Dhaka’s modern high-rises increasingly mandate smoke detectors — meaning a quiet few micrograms of americium stand guard in each tower.
Radiation-safety leaflets warn never to dismantle a smoke detector: the sealed americium is harmless where it is, but not worth breathing in.

Story

History & name

In late 1944 Glenn Seaborg’s team at the University of Chicago’s Metallurgical Laboratory — Ralph James, Leon Morgan and Albert Ghiorso — bombarded plutonium-239 with neutrons in a nuclear reactor. The plutonium swallowed successive neutrons to become plutonium-241, which beta-decayed into a brand-new element: americium-241. The discovery was classified under the Manhattan Project, and Seaborg first revealed it publicly — together with curium — on a children’s radio quiz show called “Quiz Kids” in November 1945. The name honours the Americas, deliberately echoing europium, the element named for Europe that sits directly above it in the table.

Name originNamed after the Americas, mirroring europium (named for Europe) directly above it in the table.