Tellurium at a glance
- Atomic number
- 52
- Symbol
- Te
- Atomic mass
- 127.6 u
- Category
- Metalloid
- Group / period
- 16 / 5
- Electron configuration
- [Kr] 4d 10 5s 2 5p 4
- State at 25 °C
- Solid
- Melting point
- 449.5 °C
- Boiling point
- 987.9 °C
- Density
- 6.232 g/cm³
- Electronegativity
- 2.1
- 1st ionization energy
- 869 kJ/mol
- Oxidation states
- −2, +4, +6
- Discovered
- 1782
Atomic structure
A neutral tellurium atom has 52 protons and 52 electrons, and its most common isotope carries about 78 neutrons. One atom weighs about 2.12 × 10⁻²⁵ kg, so a mole of tellurium (6.022 × 10²³ atoms) weighs 127.6 g. That nucleus holds 1.5 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 5 shells (K 2, L 8, M 18, N 18, O 6), which gives the configuration [Kr] 4d 10 5s 2 5p 4. With 6 electrons in its outer shell, it tends to gain or share electrons to complete its outer shell. It has 8 stable isotopes: Te-120, Te-122, Te-123, Te-124, Te-125, Te-126, Te-128 and Te-130. Its most common isotope, Te-130, has the same mass number as Xe-130 and Ba-130: isobars, nuclei of different elements with 130 nucleons each.
Physical properties
At room temperature (25 °C) tellurium is a solid. It melts at 449.5 °C and boils at 987.9 °C, so it stays liquid across a 538.3-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 6.232 g/cm³, 6.23 times as dense as water. Its atoms have a radius of about 140 pm (Antimony next door is 145 pm). In the solid, its atoms pack into a hexagonal lattice.
Chemical behaviour
Its electronegativity is 2.1 on the Pauling scale. Pulling off its outermost electron takes 869 kJ/mol, less than Selenium above it (941 kJ/mol). A bond between tellurium and chlorine would be polar covalent, with an electronegativity difference of 1.1. It releases 190 kJ/mol when it gains an extra electron. Its common oxidation states are −2, +4, +6, so in compounds you will usually meet it as Te²⁻, Te⁴⁺ and Te⁶⁺. Group 16 also holds Oxygen, Sulfur, Selenium, Polonium and Livermorium, which share its outer-shell pattern. Its Lewis symbol is Te surrounded by 6 dots.
Where it comes from
It makes up 0.001 mg/kg of Earth's crust, the 79th most abundant element there. It was first identified in 1782, making it the 25th element to be discovered (counting the 11 known since antiquity together).