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Zr

Zirconium

Zirconium (Zr) is a transition metal with atomic number 40 and an atomic mass of 91.222. Its electron configuration is [Kr] 4d2 5s2.

Zirconium key data

Symbol Zr
Atomic number 40
Atomic mass (standard atomic weight) 91.222
Molar mass 91.222 g/mol
Protons 40
Neutrons (most abundant isotope, zirconium-90) 50
Electrons (neutral atom) 40
Category Transition metal
Period 5
Group 4
Block d-block
Noble gas notation [Kr] 4d2 5s2
Full electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d2 5s2
Electrons per shell 2, 8, 18, 10, 2

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Measured properties of zirconium

From PubChem, the US National Institutes of Health. Public domain.

Melting point 2128 K (1854.9 °C), 16th of 103 by melting point
Boiling point 4682 K (4408.9 °C), 10th of 93 by boiling point
Density 6.52 g/cm³, 55th of 96 by density
State at room temperature Solid
Electronegativity 1.33 (Pauling), 59th of 95 by electronegativity
Van der Waals radius 186 pm, 76th of 99 by atomic radius
First ionisation energy 6.634 eV (640.1 kJ/mol), 58th of 102 by first ionisation energy
Electron affinity 0.426 eV (41.1 kJ/mol), 46th of 57 by electron affinity
Common oxidation states +4
Discovered 1789

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Zirconium electron configuration

The full electron configuration of zirconium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d2 5s2. With the noble-gas core collapsed it is [Kr] 4d2 5s2, and the outermost subshell is 5s2.

Bohr model of zirconium (Zr): a nucleus and five shells holding 2, 8, 18, 10 and 2 electrons from the inside out.
Bohr model of zirconium (Zr). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of zirconium (Zr), [Kr] 4d2 5s2, with the krypton core drawn as one bar: one box per orbital, filled by Hund’s rule, showing two unpaired electrons, in 4d.
Orbital diagram of zirconium (Zr). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one zirconium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 91.222 / (6.02214076 × 10²³)
  2. = 1.5148 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 91.222
  2. = 6.6016 × 10²¹ atoms

Zirconium on the periodic table

Zirconium is in period 5, group 4, in the d-block.

The other elements of group 4 are titanium, hafnium and rutherfordium.

The rest of period 5

Work with zirconium