What is the noble-gas shorthand for holmium?

The abbreviated notation is [Xe] 4f¹¹ 6s², where [Xe] represents the filled xenon core (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶, 54 electrons). The remaining 13 electrons are in 4f¹¹ and 6s².

How many unpaired electrons does holmium have?

Holmium has three unpaired electrons in its ground state, all in the 4f subshell. By Hund's rule, the first 7 electrons occupy the 7 orbitals singly, then 4 pair with four of them — leaving 3 singly occupied orbitals.

Is holmium an exception to the Aufbau principle?

No. Unlike gadolinium (Z=64), holmium follows the standard Aufbau order without any exception. Its configuration [Xe] 4f¹¹ 6s² matches the expected sequential filling of the 4f subshell. The adjacent gadolinium is the exception that promotes one electron to 5d for extra half-filled 4f stability; holmium does not have an analogous driver.

What oxidation state does holmium typically form?

Holmium most commonly forms the +3 ion (Ho³⁺) by losing its two 6s electrons and one 4f electron. The +2 state is rare. The +3 state is stable because removing three electrons yields a [Xe] 4f¹⁰ configuration, which has no special half-filled or fully-filled stabilization but is still energetically favorable in ionic compounds.

Why is holmium used in lasers?

The holmium-YAG (Ho:YAG) laser operates at 2.09 μm in the mid-infrared, a wavelength strongly absorbed by water in tissue. This makes it useful in minimally invasive surgery (urological, orthopedic, and ENT procedures). The lasing transition involves energy levels of the Ho³⁺ ion in the 4f¹⁰ configuration of the crystal host.

Why is holmium used in high-field magnets?

Holmium has one of the highest magnetic moments of any element. Holmium metal and holmium-iron alloys (holmium pole pieces) are used in NMR spectrometers and MRI machines to concentrate and shape strong magnetic fields. Its three unpaired 4f electrons and high spin-orbit coupling produce a large saturation magnetization at low temperatures.

Holmium Electron Configuration

Reference tool for holmium's electron configuration ([Xe] 4f¹¹ 6s²), orbital diagram, Aufbau principle context, and key properties including holmium laser and magnet uses.

Z = 67 Ho Holmium

Holmium — Electron Configuration

Atomic number 67 · Lanthanide · Period 6 · f-block · Standard Aufbau order

[Xe] 4f¹¹ 6s² 67 electrons 3 unpaired electrons Paramagnetic

Standard Aufbau filling — no exception

Holmium follows the expected filling order: after the xenon core, 11 electrons go into 4f and 2 fill 6s. Unlike gadolinium (Z=64), which promotes one electron to 5d for half-filled 4f stability, holmium has no analogous driver and stays at [Xe] 4f¹¹ 6s².

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 (part of Xe core)	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 (part of Xe core)	10	10	4d¹⁰
5s	s orbital, shell n=5	2	2	5s²
5p	p orbitals, shell n=5 (completes Xe core)	6	6	5p⁶
4f	f orbitals, shell n=4 (partially filled)	11	14	4f¹¹
6s	s orbital, shell n=6 (outermost)	2	2	6s²
Total		67

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹¹ 5s² 5p⁶ 6s²

All subshells written explicitly; 67 electrons total.

Noble-Gas Shorthand

[Xe] 4f¹¹ 6s²

[Xe] = xenon core, 54 electrons (1s² through 5p⁶). The remaining 13 electrons are 4f¹¹ + 6s².

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 4f¹¹ 29 / 32 electrons (91%)

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

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

Shell 4 holds 29 of its 32-electron maximum (4f has 11 of 14 possible electrons). Shell 5 has only 8 electrons — the 5d and 5f subshells are empty in holmium. Shell 6 has 2 electrons in 6s.

The Xenon Core — [Xe]

The first 54 electrons of holmium match the complete electron configuration of xenon (Z=54):

[Xe] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶

The remaining 13 electrons — 4f¹¹ 6s² — govern holmium's chemistry, magnetic properties, and oxidation states.

Orbital Box Diagram — Valence Region

The xenon core (1s² through 5p⁶, 54 electrons) is shown in compact form. The valence subshells 4f and 6s are shown in detail.

[Xe]

core: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶

54 electrons, all paired — xenon configuration

11 electrons: orbitals 1–4 paired, orbitals 5–7 singly occupied (3 unpaired)

2 electrons (paired) — outermost shell

Each box = one orbital. Opposing arrows = paired electrons (+½ and −½ spin). Single up arrow = unpaired electron. Colored border = partially filled subshell.

Holmium has 3 unpaired electrons, all in the 4f subshell. Together with strong spin-orbit coupling, this gives it strong paramagnetic behavior and enables use in high-field magnets and holmium lasers.

Quantum Numbers — Valence Electrons (post-[Xe])

Electron #	n	l	mₗ	mₛ	Subshell
55	6	0	0	+½	6s
56	6	0	0	−½	6s
57	4	3	-3	+½	4f
58	4	3	-2	+½	4f
59	4	3	-1	+½	4f
60	4	3	0	+½	4f
61	4	3	1	+½	4f
62	4	3	2	+½	4f
63	4	3	3	+½	4f
64	4	3	-3	−½	4f
65	4	3	-2	−½	4f
66	4	3	-1	−½	4f
67	4	3	0	−½	4f

Electrons 1–54 fill the xenon core (not shown). n = principal quantum number; l = azimuthal (3→f); mₗ = magnetic (−3 to +3 for f); mₛ = spin. The first 7 fill all 4f orbitals spin-up (Hund’s rule), then 4 pair in the lowest mₗ orbitals, leaving 3 unpaired electrons.

Identity

SymbolHo Atomic number67 Atomic mass164.930 u SeriesLanthanide Period6 Blockf-block Discovery1878 (Cleve, Soret)

Physical Properties

State (25 °C)Solid Melting point1461 °C Boiling point2600 °C Density8.79 g/cm³ ColorSilvery white Crystal structureHCP

Electronic Properties

Valence electrons13 (4f¹¹ 6s²) Unpaired electrons3 (all in 4f) Common oxidation state+3 Electronegativity1.23 (Pauling) 1st ionization energy581.0 kJ/mol Magnetic behaviorParamagnetic

Applications

Holmium-YAG (Ho:YAG) lasers at 2.09 μm — used in urology (kidney stone ablation), orthopedics, and ENT surgery because the wavelength is strongly absorbed by water in tissue.
High-field magnets — holmium pole pieces concentrate and shape magnetic fields in NMR spectrometers and MRI machines, exploiting its high saturation magnetization.
Nuclear reactor control rods — holmium has a high thermal neutron absorption cross-section, making it suitable for neutron flux control.
MRI contrast research — holmium chelates are investigated as alternatives to gadolinium-based agents, particularly for interventional MRI tracking.
Calibration standard — holmium oxide (Ho₂O₃) glass is used as a wavelength calibration standard for UV-Vis spectrophotometers due to its sharp absorption peaks.

Summary

Holmium (Ho) has atomic number 67 and the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹¹ 5s² 5p⁶ 6s², abbreviated [Xe] 4f¹¹ 6s². It follows the standard Aufbau filling order for lanthanides without any exception: after the xenon core (54 electrons), 11 electrons go into the 4f subshell and 2 fill the 6s outermost shell. With three unpaired 4f electrons, holmium is paramagnetic and is used in high-field magnets, holmium-YAG lasers (2.09 μm), and nuclear control rods due to its high neutron absorption cross-section.

How it works

The Aufbau principle fills orbitals from lowest to highest energy, placing the xenon core (1s² through 5p⁶, 54 electrons) first.
After the xenon core, electrons continue filling the 4f subshell — holmium places 11 electrons there, following the expected order without exception.
The 4f subshell holds up to 14 electrons; with 11 present, the first four orbitals are doubly occupied and the last three hold one electron each (Hund's rule).
After 4f, the 6s subshell fills with 2 electrons, completing the ground-state configuration [Xe] 4f¹¹ 6s².
The three unpaired 4f electrons contribute to holmium's magnetic moment and strong paramagnetic behavior, enabling its use in high-powered permanent magnets.
The most common oxidation state is +3 (Ho³⁺), formed by removing the two 6s electrons and one 4f electron, leaving a stable [Xe] 4f¹⁰ core.

Use cases

Quick reference for chemistry homework or exam review on lanthanide electron configurations.
Understand how 4f orbitals fill across the holmium position in the lanthanide series.
Visualize the orbital box diagram and quantum numbers for each valence electron.
Explain holmium's +3 oxidation state from its valence configuration.
Compare holmium to adjacent lanthanides (dysprosium, erbium) to see 4f-filling trends.
Teaching aid for Aufbau principle and Hund's rule applied to f-block elements.
Understand the physical basis for holmium's use in solid-state lasers and MRI contrast.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu