Chemical element · Atomic number 95

Americium

Americium in the periodic table: atomic number 95, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.

Actinide

solid

[243.061380] u

A small disc of americium 241 at high magnification under a microscope — A tiny disc of americium 241 seen under a microscope.
Image credit: Bionerd
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
Commons file Licence: CC BY 3.0

Atomic classification

Shell occupancy

Americium in the Bohr shell model

This shows the electron distribution of the neutral atom in a simplified shell model.

K · n=1: 2 electrons
L · n=2: 8 electrons
M · n=3: 18 electrons
N · n=4: 32 electrons
O · n=5: 25 electrons
P · n=6: 8 electrons
Q · n=7: 2 electrons

Shell occupancy is derived from the versioned PubChem electron configuration. Dot angles are schematic and do not represent orbitals.

Electron configuration: [Rn]7s2 5f7
Electrons per shell: 2 · 8 · 18 · 32 · 25 · 8 · 2
Group: not reported
Period: 7
Block: F
Element category: Actinide

Physical and chemical properties

Atomic mass: [243.061380] u
Standard state: solid
Density: 13.69 g/cm³
Melting point: 1,449 K
Boiling point: 2,284 K
Electronegativity: 1.3 (Pauling)
First ionisation energy: 5.993 eV
Oxidation states: +6, +5, +4, +3
Discovery: 1944

Safety and periodic classification

Safety

Safe handling cannot be inferred from Americium's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.

Position and comparison

Americium is in period 7 and the F block. Its direct neighbours by atomic number are Plutonium and Curium. The recorded Pauling electronegativity is 1.3. Periodic trends are compared only through the separately sourced neighbouring values.

Sources and scope

PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.

Where Americium sits among the 118 elements

The table compares the reported values for Americium with every other element that carries the same value in the snapshot. A rank is not a judgement, it is orientation: it says how unusual this value is across the periodic table.

Value	Americium	Position in the data set
Melting point	1,449 K	Rank 40 of 103 elements with a reported value. Highest: Carbon.
Boiling point	2,284 K	Rank 53 of 93 elements with a reported value. Highest: Rhenium.
Density	13.69 g/cm³	Rank 13 of 96 elements with a reported value. Highest: Osmium.
Electronegativity (Pauling)	1.3	Rank 63 of 95 elements with a reported value. Highest: Fluorine.
Ionisation energy	5.993 eV	Rank 79 of 102 elements with a reported value. Highest: Helium.

All values and ranks come from the PubChem Periodic Table snapshot, retrieved on 2026-07-15. Elements without a reported value are excluded, so the population differs per row.

The neighbours of Americium in the periodic table

Place in the table: No group number, period 7, F block. Classified as actinide, solid at standard conditions.
Direct neighbours: Atomic number 95. Preceded by Plutonium, followed by Curium.
Discovery: Recorded in the snapshot as: 1944. Who, where and under what circumstances is not part of that record, so this page carries the sourced year and no discovery narrative.
Oxidation states: +6, +5, +4, +3. They follow from the electron configuration [Rn]7s2 5f7 and indicate which compounds to expect.

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