What is the electron configuration of niobium?

Niobium (Nb, Z=41) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹, or in noble-gas shorthand [Kr] 4d⁴ 5s¹. This is anomalous — the Aufbau principle would predict [Kr] 4d³ 5s².

Why is niobium's electron configuration anomalous?

In Period 5 transition metals, the 4d and 5s orbital energies are very close. For niobium, placing four electrons in 4d (each singly occupied) and one in 5s achieves a lower total energy than three in 4d and two in 5s, because the exchange-energy gain from the 4d⁴ arrangement overcomes the small energy cost of promoting a 5s electron.

What is the noble-gas shorthand for niobium?

The shorthand is [Kr] 4d⁴ 5s¹, where [Kr] represents the filled krypton core (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶, Z=36).

What are niobium's common oxidation states?

Niobium most commonly exhibits +5 (the most stable, as in Nb₂O₅ and NbCl₅), +3 (in NbCl₃), and +2. The +5 state dominates because losing all five valence electrons (4d⁴ 5s¹) leaves the stable krypton core.

How many valence electrons does niobium have?

Niobium has 5 valence electrons — one in 5s and four in 4d. All five can participate in bonding, which explains the common +5 oxidation state and niobium's use as a refractory metal.

Which other elements have anomalous configurations similar to niobium?

In Period 5, molybdenum (Z=42, [Kr] 4d⁵ 5s¹), ruthenium (Z=44, [Kr] 4d⁷ 5s¹), rhodium (Z=45, [Kr] 4d⁸ 5s¹), palladium (Z=46, [Kr] 4d¹⁰), and silver (Z=47, [Kr] 4d¹⁰ 5s¹) all deviate from Aufbau. In Period 4, chromium (Z=24) and copper (Z=29) show analogous 3d/4s anomalies.

What block and period is niobium in?

Niobium is in Period 5, Group 5 (VB), and belongs to the d-block (transition metals) of the periodic table. It sits directly below vanadium in Group 5.

What is niobium used for?

Niobium is primarily used as an alloying element in high-strength low-alloy (HSLA) steels and superalloys for jet engines and gas turbines. Niobium-titanium and niobium-tin compounds are important superconductors used in MRI magnets and particle accelerators.

Niobium Electron Configuration

Name: Niobium Electron Configuration
Availability: InStock
Author: Nham Vu

Niobium (Nb, Z=41) has the anomalous electron configuration [Kr] 4d⁴ 5s¹ — not [Kr] 4d³ 5s² as Aufbau predicts. One 5s electron shifts into 4d, favoring a near-half-filled d subshell arrangement that lowers the total energy.

Anomalous configuration — Aufbau exception

Niobium does not follow the Aufbau principle. The actual ground state is [Kr] 4d⁴ 5s¹, not the predicted [Kr] 4d³ 5s². The 4d and 5s energy levels are nearly equal in Period 5; four electrons in 4d achieves a lower total energy via exchange-energy gain.

Z = 41 Nb Niobium

Niobium — Electron Configuration

Atomic number 41 · Transition metal · Period 5, Group 5 · d-block

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹ [Kr] 4d⁴ 5s¹ 41 electrons 5 valence e⁻

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 (krypton core)	10	10	3d¹⁰
4s	s orbital, shell n=4 (krypton core)	2	2	4s²
4p	p orbitals, shell n=4 (krypton core)	6	6	4p⁶
4d	d orbitals, shell n=4 (4 singly occupied)	4	10	4d⁴
5s	s orbital, shell n=5 (valence)	1	2	5s¹
Total		41

Full Configuration (actual)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹

All subshells written explicitly. Total: 41 electrons.

Noble-Gas Shorthand (actual)

[Kr] 4d⁴ 5s¹

[Kr] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (the filled krypton core, Z=36).

Aufbau Prediction (incorrect)

[Kr] 4d³ 5s²

The Aufbau rule predicts this, but the actual ground state differs.

Common Oxidation States

+2 (Nb²⁺) +3 (Nb³⁺) +5 (Nb⁵⁺)

+5 is the most stable; all five valence electrons (4d⁴ 5s¹) are removed.

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 4d⁴ 12 / 32 electrons (38%)

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

Shell 4 holds 4s² + 4p⁶ (krypton core) + 4d⁴ = 12 electrons out of a possible 32. The 4d subshell is only 40% full (4 of 10), and the anomalous 5s→4d promotion puts one electron there instead of in 5s.

Orbital Box Diagram

2 electrons (paired)

6 electrons across 3 orbitals (all paired)

2 electrons (paired)

6 electrons (krypton core starts at 3s)

10 electrons across 5 orbitals (fully paired — krypton core ends here)

2 electrons (paired, krypton core)

6 electrons (paired, krypton core complete)

empty

4 unpaired electrons — 4d⁴ (anomalous, exchange-energy stabilized)

1 electron (unpaired, spin up) — lone 5s¹ valence electron

Each box = one orbital. Opposing arrows = paired electrons (±½ spin). The four 4d orbitals are each singly occupied (spin up) — the fifth 4d orbital is empty. The 5s¹ lone electron is the first lost when niobium is oxidized. The Aufbau prediction would place two electrons in 5s and three in 4d.

Quantum Numbers for All 41 Electrons

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	5	0	0	+½	5s

n = principal quantum number; l = azimuthal (l=0 s, l=1 p, l=2 d); mₗ = magnetic; mₛ = spin. Electrons 37–41 (highlighted) are the valence-region electrons — 4d⁴ all spin-up, 5s¹ single. Electrons 1–36 form the krypton core.

Why Niobium Breaks the Aufbau Principle

Source	Configuration	4d electrons	5s electrons
Aufbau prediction	[Kr] 4d³ 5s²	3	2
Actual ground state	[Kr] 4d⁴ 5s¹	4 (singly occupied)	1

4d / 5s Energy Near-Degeneracy

In Period 5 transition metals, the 4d and 5s orbital energies are nearly identical. As the nuclear charge increases across the period, the 4d energy drops faster than 5s, so the two levels cross and re-cross. This near-degeneracy means that a single electron can sit in either orbital at negligible energy cost, and the arrangement that maximizes exchange energy wins.

Exchange Energy Stabilization

Electrons in the same subshell with parallel spins lower the system's energy through exchange interactions. Four singly occupied 4d orbitals (4d⁴, all spin-up) give 6 possible exchange pairs, contributing a larger exchange-energy stabilization than three singly occupied orbitals would. This gain is sufficient to pull one electron out of 5s into 4d, giving [Kr] 4d⁴ 5s¹.

Comparison with Chromium (Z=24)

Chromium in Period 4 achieves the analogous half-filled 3d⁵ 4s¹ state — where five singly occupied 3d orbitals give the maximum exchange-energy gain. Niobium is the Period 5 analog one group lower: it stops at four 4d electrons because its Group 5 position provides only enough electrons to half-fill four orbitals (not five as in the Group 6 molybdenum). Molybdenum (Z=42, directly below chromium) achieves [Kr] 4d⁵ 5s¹ — the true half-filled analog.

Broader Period 5 Pattern

Niobium is one of six Period 5 transition metals with anomalous configurations. Mo ([Kr] 4d⁵ 5s¹), Ru ([Kr] 4d⁷ 5s¹), Rh ([Kr] 4d⁸ 5s¹), Pd ([Kr] 4d¹⁰), and Ag ([Kr] 4d¹⁰ 5s¹) all deviate from simple Aufbau filling for the same underlying reason: 4d and 5s have similar energies and electron-electron repulsion favors spreading electrons across 4d orbitals.

Niobium Oxidation States

Nb⁵⁺

+5 state — most stable

All five valence electrons (4d⁴ 5s¹) removed; leaves the [Kr] core intact. Found in Nb₂O₅ (niobium pentoxide), NbCl₅, and niobate minerals. Dominant in industrial niobium chemistry and capacitor-grade applications.

Nb³⁺

+3 state

Three valence electrons removed; configuration [Kr] 4d². Found in NbCl₃ and niobium(III) compounds. Less common than +5; tends to disproportionate in solution.

Nb²⁺

+2 state

Two valence electrons removed; configuration [Kr] 4d³. Relatively rare; found in some halide cluster compounds and organoniobium chemistry.

Summary

How it works

The Aufbau principle normally fills 5s before 4d, predicting [Kr] 4d³ 5s² for niobium.
Instead, one 5s electron shifts into 4d, giving [Kr] 4d⁴ 5s¹ — the observed ground state.
In Period 5 transition metals, 4d and 5s orbital energies are nearly identical, making the 4d⁴ arrangement energetically competitive.
The exchange-energy gain from four singly occupied 4d orbitals (maximizing parallel spins) outweighs the cost of the 5s→4d promotion.
The result: 41 electrons arranged as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹.
Niobium is one of several Period 5 transition metals (Mo, Ru, Rh, Pd, Ag) with anomalous configurations due to the close 4d/5s energy spacing.

Use cases

Verify niobium's actual ground-state configuration versus the Aufbau prediction.
Understand why niobium is an exception to the Aufbau principle.
Study how 4d/5s energy proximity drives anomalous configurations in Period 5 metals.
Compare niobium's anomaly with the chromium (Z=24) and molybdenum (Z=42) anomalies.
Review oxidation states (+5, +3, +2) and how the d⁴ 5s¹ configuration relates to niobium's chemistry.
Use the quantum-number table for all 41 electrons in exam preparation.
Teaching aid for inorganic chemistry courses covering transition-metal electronic structure.
Explore niobium's superconducting properties in context of its electronic structure.

Frequently Asked Questions

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