Tellurium (Te)

Tellurium is the reason the periodic table is ordered by atomic number rather than atomic weight: tellurium is heavier than iodine, at 127.60 against 126.90, but must come before it to sit with the right chemical family. Mendeleev assumed the weights were simply measured wrong; Moseley's 1913 X-ray work showed the ordering principle was proton count all along. Anyone who handles tellurium ends up with garlic breath for weeks — the body methylates it into dimethyl telluride, detectable at parts per billion, and a few micrograms is enough.

Properties

Atomic number

52

Symbol

Te

Standard atomic weight

127.6 u

Category

Metalloid

Group

16

Period

5

Block

p-block

Electron configuration

[Kr] 5s² 4d¹⁰ 5p⁴

Electrons per shell

2, 8, 18, 18, 6

Melting point

722.66 K — 449.5 °C — 841.1 °F

Boiling point

1,261 K — 987.9 °C — 1810.1 °F

Density

6.232 g/cm³

Electronegativity

2.1 (Pauling)

Oxidation states

+6, +4, -2

Discovered

1782 by Franz-Joseph Müller von Reichenstein

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁴

Noble gas shorthand

[Kr] 5s² 4d¹⁰ 5p⁴

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 6

What it is used for

• Cadmium telluride thin-film solar panels
• Free-machining additive in steel and copper
• Bismuth telluride in thermoelectric coolers and camping fridges
• Rewritable optical discs, as the phase-change layer
• Vulcanising rubber and colouring glass

Hazards

• Even trace exposure produces a persistent garlic odour on breath and skin; larger doses are toxic

Neighbours in the table

Group 16

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Tellurium sits in group 16 with oxygen, sulfur, selenium, polonium, livermorium.