What is the electron configuration of rhodium?

Rhodium (Rh, Z=45) has the ground-state configuration [Kr] 4d⁸ 5s¹, or in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁸ 5s¹. It deviates from the expected [Kr] 4d⁷ 5s² because 4d⁸ 5s¹ has lower total energy.

Why is rhodium's configuration anomalous?

Simple Aufbau ordering predicts [Kr] 4d⁷ 5s². However, the exchange-energy gain from placing 8 electrons in the 4d subshell (near the symmetrically favorable d⁹ level) outweighs the cost of leaving only 1 electron in 5s. The 4d and 5s orbitals are close in energy in Period 5 transition metals, making these anomalies common.

How many valence electrons does rhodium have?

Rhodium has 9 valence electrons — 8 in 4d and 1 in 5s. In chemistry it most commonly exhibits +3 and +1 oxidation states, using its d electrons in bonding.

What block and period is rhodium in?

Rhodium is in Period 5, Group 9, and belongs to the d-block (transition metals). It is a platinum-group metal, situated between ruthenium (Z=44) and palladium (Z=46).

What is the noble-gas shorthand for rhodium?

The shorthand is [Kr] 4d⁸ 5s¹. [Kr] stands for the krypton core: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (36 electrons). The remaining 9 electrons occupy 4d (8 electrons) and 5s (1 electron).

Is rhodium paramagnetic or diamagnetic?

Rhodium is paramagnetic. Its 4d⁸ configuration has two unpaired electrons in the 4d subshell (by Hund's rule, 5 orbitals hold 8 electrons leaving 2 unpaired), giving it a net magnetic moment.

How does rhodium compare to palladium (Z=46) in configuration?

Palladium (Z=46) has the even more dramatic configuration [Kr] 4d¹⁰ — all 10 electrons fill 4d and the 5s is completely empty, making it unusual among transition metals. Rhodium at [Kr] 4d⁸ 5s¹ is one step earlier and also anomalous, but retains one electron in 5s.

Rhodium Electron Configuration

Name: Rhodium Electron Configuration
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Author: Nham Vu

Reference for rhodium's anomalous electron configuration [Kr] 4d⁸ 5s¹ (Z=45), including full subshell table, orbital box diagram, quantum numbers, and element facts.

Z = 45 Rh Rhodium

Rhodium — Electron Configuration

Atomic number 45 · Transition metal · Period 5, Group 9 · d-block

[Kr] 4d⁸ 5s¹ Full: 1s²…4d⁸ 5s¹ 45 electrons 9 valence e⁻ Anomalous config

Anomalous configuration

Aufbau predicts [Kr] 4d⁷ 5s², but the actual ground state is [Kr] 4d⁸ 5s¹. The energy gain from the near-filled 4d subshell (exchange energy) outweighs the cost of vacating one 5s electron.

Subshell Breakdown (45 electrons)

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 valence	d orbitals, shell n=4	8	10	4d⁸
5s valence	s orbital, shell n=5	1	2	5s¹
Total		45

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁸ 5s¹

All subshells written explicitly — 45 electrons total.

Noble-Gas Shorthand

[Kr] 4d⁸ 5s¹

[Kr] = 1s²…4p⁶ (krypton core, 36 electrons).

Expected vs. Actual

[Kr] 4d⁷ 5s²

[Kr] 4d⁸ 5s¹

Exchange energy favors 4d⁸ over 4d⁷.

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 4d⁸ 16 / 32 electrons (50%)

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

Shell 4 holds 16 of its maximum 32 electrons — the 4d is missing 2 electrons relative to a full subshell (4d¹⁰ would require 18 total in shell 4). Shell 5 holds only 1 electron in 5s; the 5p through 5g subshells are empty.

Period 5 Transition Metals — 4d/5s Filling

Element	Z	Configuration	Note
Yttrium (Y)	39	[Kr] 4d¹ 5s²
Zirconium (Zr)	40	[Kr] 4d² 5s²
Niobium (Nb)	41	[Kr] 4d⁴ 5s¹	Anomalous
Molybdenum (Mo)	42	[Kr] 4d⁵ 5s¹	Anomalous
Technetium (Tc)	43	[Kr] 4d⁵ 5s²
Ruthenium (Ru)	44	[Kr] 4d⁷ 5s¹	Anomalous
Rhodium (Rh) ←	45	[Kr] 4d⁸ 5s¹	Anomalous
Palladium (Pd)	46	[Kr] 4d¹⁰	Anomalous (no 5s)
Silver (Ag)	47	[Kr] 4d¹⁰ 5s¹	Anomalous

Orbital Box Diagram

Each box represents one orbital. Up-arrow = spin +½, down-arrow = spin −½. Empty = vacant.

filled

8 e⁻ across 5 orbitals — 3 fully paired, 2 singly occupied

1 electron — anomalous (expected 2)

The 4d subshell has 5 orbitals. With 8 electrons: 3 orbitals are fully paired (2e each = 6e), and 2 orbitals hold 1 electron each (2e). This leaves 2 unpaired electrons, making rhodium paramagnetic.

Quantum Numbers — All 45 Electrons

n = principal, l = azimuthal, mₗ = magnetic, mₛ = spin

e⁻ #	n	l	mₗ	mₛ	Subshell
1	1	0	0	+½	1s
2	1	0	0	−½	1s
3	2	0	0	+½	2s
4	2	0	0	−½	2s
5	2	1	-1	+½	2p
6	2	1	-1	−½	2p
7	2	1	0	+½	2p
8	2	1	0	−½	2p
9	2	1	1	+½	2p
10	2	1	1	−½	2p
11	3	0	0	+½	3s
12	3	0	0	−½	3s
13	3	1	-1	+½	3p
14	3	1	-1	−½	3p
15	3	1	0	+½	3p
16	3	1	0	−½	3p
17	3	1	1	+½	3p
18	3	1	1	−½	3p
19	3	2	-2	+½	3d
20	3	2	-2	−½	3d
21	3	2	-1	+½	3d
22	3	2	-1	−½	3d
23	3	2	0	+½	3d
24	3	2	0	−½	3d
25	3	2	1	+½	3d
26	3	2	1	−½	3d
27	3	2	2	+½	3d
28	3	2	2	−½	3d
29	4	0	0	+½	4s
30	4	0	0	−½	4s
31	4	1	-1	+½	4p
32	4	1	-1	−½	4p
33	4	1	0	+½	4p
34	4	1	0	−½	4p
35	4	1	1	+½	4p
36	4	1	1	−½	4p
37	4	2	-2	+½	4d
38	4	2	-1	+½	4d
39	4	2	0	+½	4d
40	4	2	1	+½	4d
41	4	2	2	+½	4d
42	4	2	-2	−½	4d
43	4	2	-1	−½	4d
44	4	2	0	−½	4d
45	5	0	0	+½	5s

Valence electrons (4d and 5s) are highlighted. n = principal; l = azimuthal (0→s, 1→p, 2→d); mₗ = magnetic; mₛ = spin projection.

Identity

SymbolRh Atomic number45 Atomic mass102.906 u Group9 Period5 Blockd-block CategoryTransition metal (PGM)

Physical Properties

State (25 °C)Solid Melting point1964 °C Boiling point3695 °C Density12.41 g/cm³ AppearanceSilvery-white metal Hardness (Mohs)6.0

Electronic Properties

Valence electrons9 (4d⁸ 5s¹) Common ox. states+3, +1 Electronegativity2.28 (Pauling) Ionization energy 1719.7 kJ/mol Electron affinity110.3 kJ/mol Magnetic behaviorParamagnetic

Context & Uses

Used in automotive catalytic converters alongside palladium and platinum.
One of the rarest and most valuable platinum-group metals (PGMs) on Earth.
Reflective coating for optical instruments and mirrors.
Discovered in 1803 by William Hyde Wollaston; named for the Greek word for rose (rhodon) due to its rose-colored salts.
Electroplated onto jewelry and white gold to add a bright, durable finish.

Summary

Reference for rhodium's anomalous electron configuration [Kr] 4d⁸ 5s¹ (Z=45), including full subshell table, orbital box diagram, quantum numbers, and element facts.

How it works

The Aufbau principle fills subshells in order of increasing energy: …4s → 3d → 4p → 5s → 4d…
Rhodium has 45 electrons; the [Kr] noble-gas core accounts for the first 36.
The remaining 9 electrons must fill 4d and 5s. The expected split is 4d⁷ 5s², but energy minimization favors 4d⁸ 5s¹.
The 4d⁸ 5s¹ configuration arises because a near-filled 4d subshell (8 electrons) lowers electron-electron repulsion more than the paired 5s² arrangement would.
This anomaly is similar to chromium ([Ar] 3d⁵ 4s¹) and copper ([Ar] 3d¹⁰ 4s¹) in Period 4.
Use the tabs below to explore the subshell table, orbital box diagram, and element facts.

Use cases

Quick reference for chemistry exams on transition-metal electron configurations.
Understand why rhodium deviates from the standard Aufbau prediction.
Write the correct [Kr] 4d⁸ 5s¹ notation for lab reports or homework.
Compare rhodium's anomalous configuration to palladium ([Kr] 4d¹⁰) and ruthenium ([Kr] 4d⁷ 5s¹).
Visualize how the 4d subshell fills across the second row of transition metals.
Teaching aid for Aufbau principle exceptions, Hund's rule, and exchange energy.
Verify all 45 quantum numbers for a complete electron inventory.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu