Chemical element · reference page

48Cd

Cadmium

Cadmium is element 48 (Cd), located in period 5, group 12 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d10 5s2.

Atomic number48

Standard atomic weight112.414(4)

Group12

Period5

Blockd

Electron configuration[Kr] 4d10 5s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of cadmium. 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 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 cadmium, 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 8.65 g/cm³. The melting point is 594.2 K (321.1 °C). The boiling point is 1 040 K (766.9 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where cadmium is found and used

In practice, cadmium is encountered in batteries, pigments and metal plating.

In practice

Examples of real uses

Batteries

Cadmium is used in selected battery chemistries, electrode materials or electrolytes. The exact role depends on the compound and cell design.

Pigments

Cadmium compounds provide stable colours or optical properties in paints, ceramics, plastics or glass.

Metal plating

Cadmium is used as an electroplated coating to protect surfaces, change appearance or provide specific electrical properties.

Periodic position

What its neighbours tell us

Cadmium is in period 5 and group 12. In the neighbourhood shown here, it lies between silver and indium in the same period; zinc is above it and mercury 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 · 2

Density8.65 g/cm³

Melting point594.2 K (321.1 °C)

Boiling point1 040 K (766.9 °C)

Pauling electronegativity1.69

First ionisation energy867.8 kJ/mol

Electron affinity—

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 cadmium is associated with Karl Samuel Leberecht Hermann. 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 112.414(4). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Cadmium 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

Cadmium and many cadmium compounds are toxic, especially to kidneys and lungs, and occupational exposure is strictly controlled.