What is the electron configuration of ruthenium?

Ruthenium (Ru, Z=44) has the ground-state configuration [Kr] 4d⁷ 5s¹, or in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁷ 5s¹. The [Kr] core accounts for the first 36 electrons.

Why is the ruthenium configuration [Kr] 4d⁷ 5s¹ instead of [Kr] 4d⁶ 5s²?

This is an Aufbau exception driven by exchange energy. In the 4d⁷ 5s¹ arrangement, seven d electrons can form more parallel-spin (exchange) pairs than in the 4d⁶ 5s² arrangement. The extra exchange stabilization outweighs the cost of promoting one 5s electron into 4d, making 4d⁷ 5s¹ the true ground state.

How many valence electrons does ruthenium have?

Ruthenium has 8 valence electrons: 7 in the 4d subshell and 1 in the 5s subshell. Because all d and s electrons in the outermost shells can participate in bonding, Ru commonly shows oxidation states from 0 to +8, with +2, +3, and +4 most common.

What block and period is ruthenium in?

Ruthenium is in Period 5, Group 8, and belongs to the d-block (transition metals). It sits between technetium (Z=43) and rhodium (Z=45) in the second row of transition metals.

Is ruthenium paramagnetic or diamagnetic?

Ruthenium is paramagnetic. Its 4d⁷ configuration contains unpaired electrons; by Hund's rule, the seven d electrons occupy five orbitals with the maximum number of parallel spins (five up, two paired), leaving three unpaired electrons in the ground state.

What are the common uses of ruthenium?

Ruthenium is used as a hardening agent in platinum and palladium alloys, as a catalyst in ammonia synthesis and fuel-cell electrodes, in ruthenium-based dyes for solar cells (dye-sensitized), in data storage (as a thin film on hard disks to improve magnetic layer performance), and in cancer-treatment drugs and photosensitizers for photodynamic therapy.

Ruthenium Electron Configuration

Name: Ruthenium Electron Configuration
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Author: Nham Vu

Full and shorthand electron configuration of ruthenium (Ru, Z=44): [Kr] 4d⁷ 5s¹ — an Aufbau exception — with orbital box diagram, quantum numbers, and subshell breakdown.

Z = 44 Ru Ruthenium

Ruthenium — Electron Configuration

Atomic number 44 · Transition metal · Period 5, Group 8 · d-block

[Kr] 4d⁷ 5s¹ Full: 1s²…4d⁷ 5s¹ 44 electrons 8 valence e⁻ Aufbau exception

Aufbau Exception

The simple Aufbau rule predicts [Kr] 4d⁶ 5s², but the true ground state is 4d⁷ 5s¹. Exchange energy among the seven 4d electrons lowers the total energy enough to pull one electron from 5s into 4d. This is the same principle behind the analogous anomalies in Cr (3d⁵ 4s¹) and Cu (3d¹⁰ 4s¹).

Subshell Breakdown

Subshell	Type	Electrons	Max Capacity	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 (valence)	d orbitals, shell n=4 (valence)	7	10	4d⁷
5s (valence)	s orbital, shell n=5 (valence)	1	2	5s¹
Total		44

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁷ 5s¹

All 44 electrons written explicitly.

Noble-Gas Shorthand

[Kr] 4d⁷ 5s¹

[Kr] = 1s²…4p⁶ (krypton's 36 electrons).

Predicted vs. Actual

4d⁶ 5s² (Aufbau)

4d⁷ 5s¹ (actual)

Exchange energy drives the deviation.

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 4d⁷ 15 / 32 electrons (47%)

Shell 5 (n=5) — 5s¹ 1 / 50 electrons (2%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Ruthenium fills 15 of those: the 4d subshell is partially filled with 7 of a possible 10 electrons, and 4f remains empty. Shell 5 holds only 1 electron in 5s.

Period-5 d-Block Neighbors

Element	Z	Configuration	Note
Niobium (Nb)	41	[Kr] 4d⁴ 5s¹	Exception
Molybdenum (Mo)	42	[Kr] 4d⁵ 5s¹	Exception (half-filled d)
Technetium (Tc)	43	[Kr] 4d⁵ 5s²	Regular
Ruthenium (Ru) ←	44	[Kr] 4d⁷ 5s¹	Exception
Rhodium (Rh)	45	[Kr] 4d⁸ 5s¹	Exception
Palladium (Pd)	46	[Kr] 4d¹⁰	Exception (no 5s)
Silver (Ag)	47	[Kr] 4d¹⁰ 5s¹	Exception (filled d)

Most Period-5 d-block elements deviate from the simple Aufbau rule. Ruthenium is part of a cluster where 4d⁷ 5s¹ is favored over the expected 4d⁶ 5s².

Orbital Box Diagram

Each box represents one orbital. Up-arrow = spin +½, down-arrow = spin −½. The [Kr] core (36 electrons) is collapsed for readability.

[Kr]

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ — 36 electrons (krypton core, fully paired)

7 electrons — 2 paired + 3 unpaired orbitals

1 electron (unpaired)

By Hund's rule, the 7 electrons in 4d fill all five orbitals singly first (5 up-spins), then two of those receive a second electron (down-spin). Result: 3 unpaired electrons in 4d plus 1 unpaired in 5s = 4 unpaired total, making ruthenium paramagnetic.

Quantum Numbers — Valence Electrons (4d⁷ 5s¹)

e⁻ #	n	l	mₗ	mₛ	Subshell
37	4	2	-2	+½	4d
38	4	2	-2	−½	4d
39	4	2	-1	+½	4d
40	4	2	-1	−½	4d
41	4	2	0	+½	4d
42	4	2	1	+½	4d
43	4	2	2	+½	4d
44	5	0	0	+½	5s

Electrons 1–36 occupy the [Kr] core (shown collapsed above). n = principal; l = azimuthal (l=2 → d); mₗ = magnetic; mₛ = spin. Electrons 37–43 are in 4d; electron 44 is in 5s.

Summary

Full and shorthand electron configuration of ruthenium (Ru, Z=44): [Kr] 4d⁷ 5s¹ — an Aufbau exception — with orbital box diagram, quantum numbers, and subshell breakdown.

How it works

The [Kr] core (36 electrons) fills shells 1–4 through the krypton noble-gas configuration.
The Aufbau principle would place the next 8 electrons as 4d⁶ 5s², but ruthenium adopts 4d⁷ 5s¹ instead.
Exchange energy stabilizes the 4d⁷ arrangement: seven d electrons share more parallel-spin pairs than the 4d⁶ state, lowering total energy.
The single 5s electron sits in the outermost shell, contributing to ruthenium's metallic bonding and catalytic reactivity.
Use the tabs below to explore the subshell breakdown, orbital box diagram, and element facts.

Use cases

Chemistry homework or exam questions on transition-metal electron configurations.
Understanding why ruthenium deviates from the simple Aufbau prediction.
Comparing Ru to its Period-5 neighbors (Rh, Pd, Tc, Mo) and their d-subshell anomalies.
Visualizing the partially filled 4d subshell responsible for ruthenium's catalytic properties.
Reference for quantum-number assignments across all 44 electrons.
Teaching the role of exchange energy in d-block configuration exceptions.
Studying ruthenium's use in fuel-cell catalysts, photosensitizers, and hard disk coatings.

Frequently Asked Questions

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