Chemical element · reference page

46Pd

Palladium

Palladium is element 46 (Pd), located in period 5, group 10 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d10.

Atomic number46

Standard atomic weight106.42(1)

Group10

Period5

Blockd

Electron configuration[Kr] 4d10

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of palladium. 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] 4d10, 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 palladium, 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 12.02 g/cm³. The melting point is 1 828 K (1 555 °C). The boiling point is 3 236 K (2 963 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where palladium is found and used

In practice, palladium is encountered in catalysts, electronics and hydrogen storage research.

In practice

Examples of real uses

Catalysts

Palladium is used to accelerate chemical reactions without being consumed in the overall reaction.

Electronics

Palladium is used in electronic components or materials where conductivity, semiconducting behaviour, optical response or chemical stability is useful.

Hydrogen storage research

Palladium and related materials can absorb large amounts of hydrogen, making them useful model systems for hydrogen-storage research.

Periodic position

What its neighbours tell us

Palladium is in period 5 and group 10. In the neighbourhood shown here, it lies between rhodium and silver in the same period; nickel is above it and platinum 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 · 18

Density12.02 g/cm³

Melting point1 828 K (1 555 °C)

Boiling point3 236 K (2 963 °C)

Pauling electronegativity2.2

First ionisation energy804.4 kJ/mol

Electron affinity54.24 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 palladium is associated with William Hyde Wollaston. 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 106.42(1). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Palladium 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 palladium depend on chemical form, dose and route of exposure. Pure palladium, 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.