Chemical element · reference page

72Hf

Hafnium

Hafnium is element 72 (Hf), located in period 6, group 4 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Xe] 4f14 5d2 6s2.

Atomic number72

Standard atomic weight178.486(6)

Group4

Period6

Blockd

Electron configuration[Xe] 4f14 5d2 6s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of hafnium. 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, [Xe] 4f14 5d2 6s2, 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 hafnium, 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 13.31 g/cm³. The melting point is 2 504 K (2 231 °C). The boiling point is 4 876 K (4 603 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where hafnium is found and used

In practice, hafnium is encountered in nuclear control, microelectronics and alloys.

In practice

Examples of real uses

Nuclear control

Strong neutron absorption by certain hafnium isotopes useful in reactor-control materials.

Microelectronics

Hafnium is used in thin films, gates, interconnects or semiconductor processing at very small scales.

Alloys

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

Periodic position

What its neighbours tell us

Hafnium is in period 6 and group 4. In the neighbourhood shown here, tantalum is immediately to its right in the same period; zirconium is above it and rutherfordium 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 · 32 · 10 · 2

Density13.31 g/cm³

Melting point2 504 K (2 231 °C)

Boiling point4 876 K (4 603 °C)

Pauling electronegativity1.3

First ionisation energy658.5 kJ/mol

Electron affinity17.18 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 hafnium is associated with Dirk Coster. 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 178.486(6). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Hafnium 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 hafnium depend on chemical form, dose and route of exposure. Pure hafnium, 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.