All practice pages/Interatomic theory/Elements
Element 52, a metalloid
One of the rarest stable elements in the crust, named for the Earth, and a key ingredient in thin-film solar panels.
Period 5, group 16. The other metalloids are tinted, and every cell opens its own article.
Tellurium has 52 electrons, one for every proton, so the atom carries no charge. Below are the same 52 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁴
Short form: [Kr] 4d¹⁰ 5s² 5p⁴, where [Kr] stands for the 36 electrons krypton already has.
That list runs by shell. In the order the subshells fill it reads [Kr] 5s² 4d¹⁰ 5p⁴, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 3 here is 3s² 3p⁶ 3d¹⁰, and 2 + 6 + 10 is 18.
Tellurium sits in period 5 and has 5 shells. The period number counts the shells.
The outer shell holds 6 electrons. Those are the ones tellurium can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 16 means 6.
A metalloid: it tends to share electrons in covalent bonds rather than give them up completely.
About as rare in the crust as gold and platinum. It turns up in gold ores as tellurides such as calaverite (AuTe₂), and it is recovered from the sludge left when copper is refined.
Franz-Joseph Müller von Reichenstein found it in 1782 in a gold ore from Transylvania. Martin Heinrich Klaproth confirmed it in 1798 and named it from the Latin tellus, earth.
Cadmium telluride thin-film solar panels now take a large share. Bismuth telluride makes thermoelectric coolers and generators, tellurium alloys store data in rewritable optical discs, and small additions make steel and copper easier to machine and help cure rubber.
Even small exposures give the breath and sweat a strong garlic smell for weeks, from a compound the body makes out of it. Larger amounts are toxic.