Chemical element · reference page

52Te

Tellurium

Tellurium is element 52 (Te), located in period 5, group 16 and the p block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d10 5s2 5p4.

Atomic number52

Standard atomic weight127.60(3)

Group16

Period5

Blockp

Electron configuration[Kr] 4d10 5s2 5p4

Electronic structure

What controls its chemistry

Group 16 atoms have six valence electrons. Bonding often involves gaining or sharing two electrons, while the heavier members can access a wider range of oxidation states.

For tellurium, this outer-shell structure helps explain the importance of oxides, sulfides, oxoanions and covalent compounds across the chalcogen family.

Chemical forms

Compounds, ions and materials

Hydrides, oxides, sulfides or selenides, halides and oxoanions are important across group 16. The −2 oxidation state is common for the lighter chalcogens, while positive oxidation states become increasingly accessible in heavier compounds.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 6.24 g/cm³. The melting point is 722.7 K (449.6 °C). The boiling point is 1 261 K (987.9 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where tellurium is found and used

In practice, tellurium is encountered in solar cells, thermoelectric materials and alloys.

In practice

Examples of real uses

Solar cells

Tellurium is used in photovoltaic absorbers, contacts, coatings or semiconductor layers that convert light into electrical energy.

Thermoelectric materials

Tellurium is used in materials that convert a temperature difference directly into electrical voltage, or the reverse.

Alloys

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

Periodic position

What its neighbours tell us

Tellurium is in period 5 and group 16. In the neighbourhood shown here, it lies between antimony and iodine in the same period; selenium is above it and polonium 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

Classificationmetalloid

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 18 · 6

Density6.24 g/cm³

Melting point722.7 K (449.6 °C)

Boiling point1 261 K (987.9 °C)

Pauling electronegativity2.1

First ionisation energy869.3 kJ/mol

Electron affinity190.2 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 tellurium is associated with Franz-Joseph Müller von Reichenstein. 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 127.60(3). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Tellurium 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 tellurium depend on chemical form, dose and route of exposure. Pure tellurium, 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.