Chemical element · reference page

40Zr

Zirconium

Zirconium is element 40 (Zr), located in period 5, group 4 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d2 5s2.

Atomic number40

Standard atomic weight91.222(3)

Group4

Period5

Blockd

Electron configuration[Kr] 4d2 5s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of zirconium. Transition metals can use electrons of similar energies in bonding, which is why variable oxidation states, coordination compounds and catalytic behaviour are common across the d block.

Its electron configuration, [Kr] 4d2 5s2, should be read together with the oxidation state of the compound: removing electrons changes which d orbitals are occupied and can alter colour, magnetism, bonding and reactivity.

Chemical forms

Compounds, ions and materials

For zirconium, important chemical forms include metals and alloys, oxides, halides and coordination compounds. Variable oxidation states are common because s and d electrons have similar energies, and ligands around the metal ion can strongly alter colour, magnetism and reactivity.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 6.52 g/cm³. The melting point is 2 128 K (1 855 °C). The boiling point is 4 650 K (4 377 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where zirconium is found and used

In practice, zirconium is encountered in nuclear reactors, ceramics and alloys.

In practice

Examples of real uses

Nuclear reactors

Zirconium is used in reactor materials, fuels, neutron control or specialised nuclear systems depending on the isotope and chemical form.

Ceramics

Zirconium is used in ceramic compounds chosen for heat resistance, hardness, electrical behaviour or colour.

Alloys

Zirconium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Periodic position

What its neighbours tell us

Zirconium is in period 5 and group 4. In the neighbourhood shown here, it lies between yttrium and niobium in the same period; titanium is above it and hafnium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationtransition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 10 · 2

Density6.52 g/cm³

Melting point2 128 K (1 855 °C)

Boiling point4 650 K (4 377 °C)

Pauling electronegativity1.33

First ionisation energy640.1 kJ/mol

Electron affinity41.81 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of zirconium is associated with Martin Heinrich Klaproth. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 91.222(3). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Zirconium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with zirconium depend on chemical form, dose and route of exposure. Pure zirconium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.