What is the electron configuration of zirconium?

Zirconium (Zr, Z=40) has the ground-state electron configuration [Kr] 4d² 5s², which expands to 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s². All 40 electrons are distributed across ten filled or partially filled subshells.

What noble gas core does zirconium use?

Zirconium uses [Kr] (krypton, Z=36) as its noble-gas core. The [Kr] shorthand represents 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶, which accounts for 36 of zirconium's 40 electrons.

Why is the 5s subshell written before 4d in zirconium's configuration?

The 5s subshell has slightly lower energy than 4d and fills first according to the Aufbau principle. Textbooks therefore write the configuration as [Kr] 4d² 5s² (subshells listed in n,l order) or equivalently [Kr] 5s² 4d² (listed in fill order). Both are accepted; the standard IUPAC form lists subshells by increasing n, then l.

How many valence electrons does zirconium have?

Zirconium has four valence electrons: two in the 4d subshell and two in the 5s subshell (4d² 5s²). These are the electrons available for bonding, which is why zirconium commonly forms +4 oxidation-state compounds.

What block and group is zirconium in?

Zirconium is in Period 5, Group 4, and belongs to the d-block (transition metals) of the periodic table. It sits directly below titanium and above hafnium in Group 4.

What is zirconium's most common oxidation state?

Zirconium most commonly forms the +4 oxidation state (Zr⁴⁺), losing all four valence electrons (4d² 5s²). The +2 and +3 states exist but are rare and strongly reducing.

Is zirconium paramagnetic or diamagnetic?

Zirconium is paramagnetic in its ground state. It has two unpaired 4d electrons (one in each of two separate 4d orbitals, per Hund's rule), giving it a net magnetic moment and making it weakly attracted to magnetic fields.

Zirconium Electron Configuration

Reference for zirconium's ground-state electron configuration ([Kr] 4d² 5s²), full subshell table, orbital box diagram, quantum numbers, and element properties.

Z = 40 Zr Zirconium

Zirconium — Electron Configuration

Atomic number 40 · Transition metal · Period 5, Group 4 · d-block

[Kr] 4d² 5s² 40 electrons 4 valence e⁻ d-block Paramagnetic

Subshell Breakdown

Subshell	Type	Electrons	Capacity	Notation	Part of
1s	s orbital, n=1	2	2	1s²	[Kr] core
2s	s orbital, n=2	2	2	2s²	[Kr] core
2p	p orbitals, n=2	6	6	2p⁶	[Kr] core
3s	s orbital, n=3	2	2	3s²	[Kr] core
3p	p orbitals, n=3	6	6	3p⁶	[Kr] core
3d	d orbitals, n=3	10	10	3d¹⁰	[Kr] core
4s	s orbital, n=4	2	2	4s²	[Kr] core
4p	p orbitals, n=4	6	6	4p⁶	[Kr] core
4d	d orbitals, n=4	2	10	4d²	valence
5s	s orbital, n=5	2	2	5s²	valence
Total		40

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s²

All 10 subshells written explicitly (40 electrons).

Noble-Gas Shorthand

[Kr] 4d² 5s²

[Kr] replaces the first 36 electrons.

Valence Electrons

4d² 5s²

4 valence electrons; common oxidation state +4.

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 4d² 10 / 32 electrons (31%)

Shell 5 (n=5) — 5s² 2 / 50 electrons (4%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Zirconium fills only 10 of those (the 4f is empty). Shell 5 has only 2 electrons in the 5s — the 5p, 5d, and 5f subshells remain empty.

Zirconium in Context — Period 5 Transition Metals

Element	Z	Configuration
Yttrium (Y)	39	[Kr] 4d¹ 5s²
Zirconium (Zr) ← this element	40	[Kr] 4d² 5s²
Niobium (Nb)	41	[Kr] 4d⁴ 5s¹
Molybdenum (Mo)	42	[Kr] 4d⁵ 5s¹
Technetium (Tc)	43	[Kr] 4d⁵ 5s²
Ruthenium (Ru)	44	[Kr] 4d⁷ 5s¹

Note how Nb and Mo deviate from the expected pattern by promoting one 5s electron to 4d, achieving extra stability from half-filled or fully filled d subshells.

Orbital Box Diagram

[Kr] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ — 36 electrons, all paired

The krypton core is fully filled. All 18 orbitals within [Kr] hold paired electrons. Only the valence subshells (4d and 5s) are shown in detail below.

2 electrons (unpaired, one per orbital) — Hund's rule

2 electrons (paired, opposite spins) — filled

Zirconium's two 4d electrons each occupy a separate 4d orbital (Hund's rule — parallel spins minimize repulsion). The 5s orbital is fully paired. This gives zirconium two unpaired electrons and makes it paramagnetic.

Quantum Numbers — Valence Electrons (37–40)

e⁻ #	n	l	mₗ	mₛ	Subshell	Paired?
37	5	0	0	+½	5s	No (partner below)
38	5	0	0	−½	5s	Yes (paired)
39	4	2	-2	+½	4d	No (unpaired)
40	4	2	-1	+½	4d	No (unpaired)

Electrons 1–36 belong to the [Kr] core (all paired). n = principal; l = azimuthal (0→s, 2→d); mₗ = magnetic; mₛ = spin. The two unpaired 4d electrons are the source of zirconium's paramagnetism.

Identity

SymbolZr Atomic number40 Atomic mass91.224 u Group4 (Ti group) Period5 Blockd-block CategoryTransition metal

Physical Properties

State (25 °C)Solid Melting point1855 °C Boiling point4409 °C Density6.52 g/cm³ ColorSilvery-grey metal Crystal structureHexagonal (hcp)

Electronic Properties

Valence electrons4 (4d² 5s²) Oxidation states+4, +3, +2 (rare) Electronegativity1.33 (Pauling) Ionization energy 1640.1 kJ/mol Electron affinity41.1 kJ/mol Magnetic behaviorParamagnetic

Context & Uses

Used extensively as nuclear reactor fuel cladding (zircaloy) due to very low neutron absorption.
Zirconia (ZrO₂) is a tough ceramic used in dental crowns and cutting tools.
Cubic zirconia (CZ) is a widely used diamond simulant in jewelry.
Discovered in 1789 by Martin Klaproth in zircon gemstones; isolated in pure form by Berzelius in 1824.
Highly corrosion-resistant — forms a thin, self-healing ZrO₂ oxide layer on its surface.

Summary

Zirconium (Zr) has atomic number 40 and the ground-state electron configuration [Kr] 4d² 5s², or in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s². It is a d-block transition metal in Period 5, Group 4, with two electrons in the 4d subshell and two in the 5s subshell beyond the krypton core. This tool provides the complete subshell breakdown, an orbital box diagram, quantum numbers for all 40 electrons, and key element properties.

How it works

The Aufbau principle fills subshells in order of increasing energy, following the n+l rule.
Krypton (Z=36) forms the noble-gas core [Kr] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶.
The next four electrons (Z=37 through 40) enter the 5s and 4d subshells in energy order.
Zirconium's 40th electron configuration ends with [Kr] 4d² 5s² — two paired electrons in 5s, two electrons spread across the 4d orbitals.
Because the 5s fills before 4d (energy ordering), 5s² is written first in some textbooks and 4d² second.
Use the tabs below to explore the full configuration table, orbital diagram, and element facts.

Use cases

Chemistry homework requiring the electron configuration of zirconium in both full and abbreviated form.
Verify the correct placement of zirconium's 4d and 5s electrons relative to the [Kr] core.
Understand why zirconium belongs to the d-block and Group 4 of the periodic table.
Visualize the partially filled 4d subshell and its two electrons via the orbital box diagram.
Look up quantum numbers for each of the 40 electrons in zirconium.
Compare zirconium's configuration to neighboring transition metals yttrium and niobium.
Teaching aid for Aufbau principle, Hund's rule, and the d-block filling order.
Reference for materials science and nuclear engineering courses where zirconium alloys appear.

Frequently Asked Questions

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