Transition metalElement 40 · d-block

Zirconium (Zr)

Zirconium (Zr) is a transition metal with atomic number 40 and a standard atomic weight of 91.222. At room temperature it is a solid that melts at 1,854 °C and boils at 4,406 °C.

40ZrZirconium91.222

Atomic number

protons

Atomic weight

91.222

CIAAW 2024

Melting point

1,854 °C

2,127.15 K

Boiling point

4,406 °C

4,679.15 K

Density

6.52 g/cm³

near room temperature

Electronegativity

1.33

Pauling scale

State at 25 °C

Solid

Discovered

1789

Germany

Zirconium at a glance

Identity

Symbol	Zr
Atomic number (Z)	40
Atomic weight	91.222 ± 0.003 (CIAAW 2024)
Category	Transition metal
Group	4
Period	5
Block	d-block
CAS number	7440-67-7

Atomic properties

Electron configuration	[Kr] 4d² 5s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s²
Electrons per shell	2, 8, 18, 10, 2
Oxidation states	+4 Less common: +1, +2, +3
Electronegativity (Pauling)	1.33
First ionisation energy	6.634 eV (640.1 kJ/mol) 2nd: 13.13 eV · 3rd: 23.17 eV
Electron affinity	0.426 eV
Atomic radius (empirical)	155 pm
Covalent radius	154 pm
Van der Waals radius	223 pm

Physical properties

State at 25 °C	Solid
Melting point	1,854 °C · 3,369.2 °F · 2,127.15 K
Boiling point	4,406 °C · 7,962.8 °F · 4,679.15 K
Density	6.52 g/cm³
Specific heat capacity	0.278 J/(g·K)
Thermal conductivity	22.7 W/(m·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	⁹⁰Zr 51.45%, ⁹⁴Zr 17.38%, ⁹²Zr 17.15%, ⁹¹Zr 11.22%, ⁹⁶Zr 2.8% (radioactive)
Stable isotopes	4
Known isotopes	37
Abundance in Earth's crust	165 mg/kg
Abundance in seawater	0.00003 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Zirconium electron configuration

Zirconium has 40 electrons. Written in short form, its ground-state configuration is [Kr] 4d² 5s² — the electrons of the noble gas krypton, plus 4d² 5s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s².

4d↑↑

5s↑↓

Discovery and name

Discovered

1789 — Martin Heinrich Klaproth (isolated by Berzelius, 1824) · Germany.

Name

Persian zargun, gold-coloured (via the mineral zircon).

Known for

Highly corrosion-resistant and nearly transparent to neutrons, so used to clad nuclear fuel. Cubic zirconia (ZrO₂) is a diamond simulant.

Isotopes of zirconium

Naturally occurring zirconium is a mix of 5 isotopes. Each has 40 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
⁹⁰Zr	40	50	51.45%	stable
⁹⁴Zr	40	54	17.38%	stable
⁹²Zr	40	52	17.15%	stable
⁹¹Zr	40	51	11.22%	stable
⁹⁶Zr	40	56	2.8%	radioactive · half-life 23.4 × 10¹⁸ years

37 isotopes of zirconium are known in our data set (half-lives as published in nuclear data tables).

Zirconium compared with group 4

The other elements in group 4, from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Titanium	22	47.867	1,670 °C	3,287 °C	4.506 g/cm³	1.54
Zirconium	40	91.222	1,854 °C	4,406 °C	6.52 g/cm³	1.33
Hafnium	72	178.49	2,233 °C	4,600 °C	13.3 g/cm³	1.3
Rutherfordium	104	[267]	—	—	23.3 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of zirconium?

The standard atomic weight of zirconium is 91.222 ± 0.003 (CIAAW 2024), so one mole weighs about 91.222 grams.

How many protons, neutrons and electrons does zirconium have?

A neutral zirconium atom has 40 protons and 40 electrons. Its most common isotope, zirconium-90, has 50 neutrons.

What is the electron configuration of zirconium?

[Kr] 4d² 5s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d² 5s²).

What are the melting and boiling points of zirconium?

Zirconium melts at 1,854 °C (3,369.2 °F) and boils at 4,406 °C (7,962.8 °F).

Is zirconium a metal?

Zirconium is a metal. It is in group 4, period 5, and is a solid at room temperature.

Who discovered zirconium?

1789 — Martin Heinrich Klaproth (isolated by Berzelius, 1824) (Germany).