Legend The chalcogens (ore forming) (/ˈkælkədʒənz/ KAL-kə-jənz) are the chemical elements in group 16 of the periodic table.

[16] Isotopes with nonzero nuclear spins are more abundant in nature among the chalcogens selenium and tellurium than they are with sulfur.

In 1+ cations, such as H3O+, a chalcogen forms three molecular orbitals arranged in a trigonal pyramidal fashion and one lone pair.

For example, pyrite (FeS2) is an iron ore, and the rare mineral calaverite is the ditelluride (Au, Ag)Te2.

While these compounds do exist, analogous chemicals that contain lanthanum, praseodymium, gadolinium, holmium, terbium, or ytterbium have not been discovered, as of 2008.

These compounds have numerous applications, including organo-phosphate insecticides, strike-anywhere matches and quantum dots.

[citation needed] The decrease in the number of chalcogen-phosphorus compounds further down the periodic table is due to diminishing bond strength.

Compounds in the form of M-E, where M is silicon, germanium, or tin, and E is sulfur, selenium or tellurium have been discovered.

In the 1700s and 1800s, scientists Joseph Louis Gay-Lussac and Louis-Jacques Thénard proved sulfur to be a chemical element.

Robert Hooke, Mikhail Lomonosov, Ole Borch, and Pierre Bayden all successfully created oxygen, but did not realize it at the time.

Oxygen was discovered by Joseph Priestley in 1774 when he focused sunlight on a sample of mercuric oxide and collected the resulting gas.

In 1796, Müller sent part of the sample to the German chemist Martin Klaproth, who purified the undiscovered element.

[2][42] Three of the chalcogens (sulfur, selenium, and tellurium) were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner as having similar properties.

[13] Around 1865 John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to the octaves of music.

After 1869, Dmitri Mendeleev proposed his periodic table placing oxygen at the top of "group VI" above sulfur, selenium, and tellurium.

Prior to the invention of particle accelerators, the only way to produce polonium was to extract it over several months from uranium ore.[2] The first attempt at creating livermorium was from 1976 to 1977 at the LBNL, who bombarded curium-248 with calcium-48, but were not successful.

[47] The name chalcogen comes from the Greek words χαλκος (chalkos, literally "copper"), and γενές (genes, born,[50] gender, kindle).

Chalcophile elements are those that remain on or close to the surface because they combine readily with chalcogens other than oxygen, forming compounds which do not sink into the core.

[62] Goldschmidt classification: Lithophile Siderophile Chalcophile Atmophile Trace/Synthetic Approximately 100 million metric tons of oxygen are produced yearly.

In 1865 a large deposit of elemental sulfur was discovered in the U.S. states of Louisiana and Texas, but it was difficult to extract at the time.

Historically, machines such as photocopiers and light meters used one-third of all selenium produced, but this application is in steady decline.

The secondary bonding interactions of the larger chalcogens, selenium and tellurium, can create organic solvent-holding acetylene nanotubes.

Metallic redox centers of biological importance are tunable by interactions of ligands containing chalcogens, such as methionine and selenocysteine.

Most tellurium in the blood stream is excreted slowly in urine, but some is converted to dimethyl telluride and released through the lungs.

For instance, sports divers have occasionally drowned from convulsions caused by breathing pure oxygen at a depth of more than 10 meters (33 feet) underwater.

[2] Selenium is a trace nutrient required by humans on the order of tens or hundreds of micrograms per day.

Extended, low-level exposure, which can occur at some industries, results in weight loss, anemia, and dermatitis.

As little as 10 micrograms of tellurium per cubic meter of air can cause notoriously unpleasant breath, described as smelling like rotten garlic.

[7] Acute tellurium poisoning can cause vomiting, gut inflammation, internal bleeding, and respiratory failure.

If ingested, polonium-210 is a million times as toxic as hydrogen cyanide by weight; it has been used as a murder weapon in the past, most famously to kill Alexander Litvinenko.