Tellurium (Te)
Tellurium (Te) is a metalloid with atomic number 52 and a standard atomic weight of 127.60. At room temperature it is a solid that melts at 450 °C and boils at 988 °C.
Tellurium key facts
Tellurium at a glance
Identity
| Symbol | Te |
|---|---|
| Atomic number (Z) | 52 |
| Atomic weight | 127.60 ± 0.03 (CIAAW 2024) |
| Category | Metalloid |
| Group | 16 — chalcogens (oxygen group) |
| Period | 5 |
| Block | p-block |
| CAS number | 13494-80-9 |
Atomic properties
| Electron configuration | [Kr] 4d10 5s2 5p4 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p4 |
|---|---|
| Electrons per shell | 2, 8, 18, 18, 6 |
| Oxidation states | -2, +2, +4, +6 Less common: -1, 0, +1, +3, +5 |
| Electronegativity (Pauling) | 2.1 |
| First ionisation energy | 9.01 eV (869.3 kJ/mol) 2nd: 18.6 eV · 3rd: 27.84 eV |
| Electron affinity | 1.971 eV |
| Atomic radius (empirical) | 140 pm |
| Covalent radius | 136 pm |
| Van der Waals radius | 206 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 449.5 °C · 841.1 °F · 722.66 K |
| Boiling point | 988 °C · 1,810.4 °F · 1,261.15 K |
| Density | 6.232 g/cm³ |
| Specific heat capacity | 0.202 J/(g·K) |
| Thermal conductivity | 14.3 W/(m·K) |
| Crystal structure | Hexagonal |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 130Te 34.08% (radioactive), 128Te 31.74% (radioactive), 126Te 18.84%, 125Te 7.07%, 124Te 4.74%, 122Te 2.55% |
| Stable isotopes | 6 |
| Known isotopes | 42 |
| Abundance in Earth's crust | 0.001 mg/kg |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Tellurium electron configuration
Tellurium has 52 electrons. Written in short form, its ground-state configuration is [Kr] 4d10 5s2 5p4 — the electrons of the noble gas krypton, plus 4d10 5s2 5p4.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p4.
As a member of group 16 it has 6 valence electrons in its outer shell (shell 5), which largely decide its chemistry.
Discovery and name
1782 — Franz-Joseph Müller von Reichenstein · Transylvania (today Romania).
Latin tellus, Earth.
Known for
Used in cadmium telluride solar panels, thermoelectric devices and rewritable optical discs. Rarer than platinum in Earth's crust.
Isotopes of tellurium
Naturally occurring tellurium is a mix of 8 isotopes. Each has 52 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 130Te | 52 | 78 | 34.08% | radioactive · half-life 791 × 10¹⁸ years |
| 128Te | 52 | 76 | 31.74% | radioactive · half-life 2.25 × 10²⁴ years |
| 126Te | 52 | 74 | 18.84% | stable |
| 125Te | 52 | 73 | 7.07% | stable |
| 124Te | 52 | 72 | 4.74% | stable |
| 122Te | 52 | 70 | 2.55% | stable |
| 123Te | 52 | 71 | 0.89% | stable |
| 120Te | 52 | 68 | 0.09% | stable |
42 isotopes of tellurium are known in our data set (half-lives as published in nuclear data tables).
Tellurium compared with group 16
The other elements in group 16 (chalcogens (oxygen group)), from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Oxygen | 8 | 15.999 | -219 °C | -183 °C | 1.429 g/L | 3.44 |
| Sulfur | 16 | 32.06 | 115 °C | 445 °C | 2.07 g/cm³ | 2.58 |
| Selenium | 34 | 78.971 | 221 °C | 685 °C | 4.809 g/cm³ | 2.55 |
| Tellurium | 52 | 127.60 | 450 °C | 988 °C | 6.232 g/cm³ | 2.1 |
| Polonium | 84 | [209] | 254 °C | 962 °C | 9.2 g/cm³ | 2 |
| Livermorium | 116 | [293] | — | — | 12.9 g/cm³ (pred.) | — |