What is the noble-gas shorthand for promethium?

[Xe] 4f⁵ 6s². The [Xe] core represents the 54-electron xenon configuration (1s² through 5p⁶). The remaining 7 electrons are 4f⁵ 6s².

How many valence electrons does promethium have?

Promethium has 2 valence electrons in the 6s subshell. The 4f electrons are inner (core-like) electrons and do not typically participate in bonding, though all lanthanides can access a +3 state by losing two 6s and one 4f electron.

Why is promethium radioactive?

All 61 nuclides of promethium have an unstable proton-to-neutron ratio. The nucleus spontaneously undergoes beta decay or electron capture to reach stability. The longest-lived isotope, Pm-145, has a half-life of about 17.7 years.

What block and period is promethium in?

Promethium is in Period 6, Group 3 (lanthanide series), and belongs to the f-block. It is the 4th element of the lanthanide series (La, Ce, Pr, Nd, Pm…).

How was promethium discovered?

Promethium was first produced artificially in 1945 by Jacob Marinsky, Lawrence Glendenin, and Charles Coryell at Oak Ridge National Laboratory by separating it from uranium fission products. It was the last element with Z < 84 whose discovery was confirmed.

What oxidation state does promethium commonly have?

The most common oxidation state is +3 (Pm³⁺), formed by losing the two 6s electrons and one 4f electron. This is typical for all lanthanides and gives the [Xe] 4f⁴ ion configuration.

Promethium Electron Configuration

Name: Promethium Electron Configuration
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Complete electron configuration reference for Promethium (Pm, Z=61): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s², or [Xe] 4f⁵ 6s² in noble-gas shorthand.

Z = 61 Pm Promethium

Promethium — Electron Configuration

Atomic number 61 · Lanthanide (f-block) · Period 6 · Radioactive

[Xe] 4f⁵ 6s² 61 electrons 2 valence e⁻ No stable isotopes

Radioactive element. Promethium has no stable isotopes. The longest-lived isotope is Pm-145 (half-life ~17.7 years). Trace amounts occur naturally as fission products; it must otherwise be produced artificially in nuclear reactors.

Subshell Breakdown

Subshell	Type	Electrons	Max	Notation
1s	s orbital, shell n=1	2	2	1s²
2s	s orbital, shell n=2	2	2	2s²
2p	p orbitals, shell n=2	6	6	2p⁶
3s	s orbital, shell n=3	2	2	3s²
3p	p orbitals, shell n=3	6	6	3p⁶
3d	d orbitals, shell n=3	10	10	3d¹⁰
4s	s orbital, shell n=4	2	2	4s²
4p	p orbitals, shell n=4	6	6	4p⁶
4d	d orbitals, shell n=4	10	10	4d¹⁰
4f	f orbitals, shell n=4	5	14	4f⁵ (inner)
5s	s orbital, shell n=5	2	2	5s²
5p	p orbitals, shell n=5	6	6	5p⁶
6s	s orbital, shell n=6	2	2	6s² (valence)
Total		61

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s²

All 13 subshells written explicitly.

Noble-Gas Shorthand

[Xe] 4f⁵ 6s²

[Xe] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ (54 electrons).

Shell Fill Summary

Shell 1 (n=1) — 1s² 2 / 2 electrons (100%)

Shell 2 (n=2) — 2s² 2p⁶ 8 / 8 electrons (100%)

Shell 3 (n=3) — 3s² 3p⁶ 3d¹⁰ 18 / 18 electrons (100%)

Shell 4 (n=4) — 4s² 4p⁶ 4d¹⁰ 4f⁵ 23 / 32 electrons (72%)

Shell 5 (n=5) — 5s² 5p⁶ 8 / 50 electrons (16%)

Shell 6 (n=6) — 6s² 2 / 72 electrons (3%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Promethium's 4f subshell is half-filled (5 of 14 slots).

Orbital Box Diagram

Each box = one orbital. Two opposing arrows = paired electrons (spins +½ and −½). Single arrow = unpaired (spin up by convention).

Inner Core [Xe] — 54 electrons

filled

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ — all orbitals fully paired

—

5 of 7 orbitals each hold 1 electron (Hund's rule — all spin up).

2 orbitals empty. Not a half-filled subshell (14/2=7).

2 electrons paired — valence shell

Quantum Numbers — Outermost 7 Electrons (4f⁵ 6s²)

Electron	n	l	mₗ	mₛ	Subshell
55	4	3	-3	+½	4f
56	4	3	-2	+½	4f
57	4	3	-1	+½	4f
58	4	3	0	+½	4f
59	4	3	1	+½	4f
60	6	0	0	+½	6s
61	6	0	0	−½	6s

l=3 (f orbitals), mₗ ranges from −3 to +3. The 5 unpaired 4f electrons each have mₛ=+½ per Hund's rule. Electrons 1–54 fill the [Xe] core.

Summary

Complete electron configuration reference for Promethium (Pm, Z=61): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s², or [Xe] 4f⁵ 6s² in noble-gas shorthand.

How it works

The Aufbau principle fills orbitals in order of increasing energy.
Promethium's 61 electrons fill through the 4f subshell, placing it in the lanthanide (f-block) series.
The 4f subshell holds 5 electrons across 7 available orbitals; by Hund's rule each occupies a separate orbital with parallel spins.
Noble-gas shorthand replaces the filled [Xe] core (54 electrons) with the symbol [Xe], leaving [Xe] 4f⁵ 6s².
Promethium has no known stable isotopes — its nucleus has an inherently unstable proton-to-neutron ratio.
The interactive tabs let you explore the full configuration, orbital diagram, and element data separately.

Use cases

Quick reference for chemistry or nuclear physics homework.
Understand how f-block lanthanides fill the 4f subshell.
Compare Promethium's configuration to neighboring lanthanides Neodymium (Z=60) and Samarium (Z=62).
Study how Hund's rule applies to a half-filled 4f subshell.
Teaching aid for radioactive elements and nuclear stability.
Verify quantum numbers for all 61 electrons.
Learn why Promethium was the last naturally occurring element to be discovered.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu