Chalcogen

The four non-radioactive chalcogens at standard temperature and pressure.

The chalcogens (/ˈkælkədʒn/) are the chemical elements in group 16 (old-style: VIB or VIA) of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), the radioactive element polonium (Po), and the synthetic element livermorium (Lv).

Although all group 16 elements of the periodic table, including oxygen, are defined as chalcogens, oxygen and oxides are usually distinguished from chalcogens and chalcogenides. The term chalcogenide is more commonly reserved for sulfides, selenides, and tellurides, rather than for oxides. Binary compounds of the chalcogens are called chalcogenides (rather than chalcides; however, this breaks the pattern of halogen/halide and pnictogen/pnictide).

Although the word "chalcogen" is literally taken from Greek words being "copper-former", the meaning is more in line with "copper-ore former" or more generally, "ore-former". These electronegative elements are strongly associated with metal-bearing minerals, where they have formed water-insoluble compounds with the metals in the ores.

Properties

Members of this group show similar patterns in their electron configuration, especially the outermost shells, resulting in similar trends in chemical behavior:

Z	Element	No. of electrons/shell
8	oxygen	2, 6
16	sulfur	2, 8, 6
34	selenium	2, 8, 18, 6
52	tellurium	2, 8, 18, 18, 6
84	polonium	2, 8, 18, 32, 18, 6
116	livermorium	2, 8, 18, 32, 32, 18, 6

Oxygen, sulfur, and selenium are nonmetals, and tellurium and polonium are metalloid semiconductors (that means, their electrical properties are between those of a metal and an insulator). Nevertheless, tellurium, as well as selenium, is often referred to as a metal when in elemental form.

Metal chalcogens are common as minerals. For example, pyrite (FeS₂) is an iron ore. The rare mineral calaverite is the ditelluride AuTe₂.

The formal oxidation number of the most common chalcogen compounds is −2. Other values, such as −1 in pyrite, can be attained. The highest formal oxidation number +6 is found in sulfates, selenates and tellurates, such as in sulfuric acid or sodium selenate (Na₂SeO₄).

Explanation of above periodic table slice:

bgcolor="Template:Element color/Other nonmetals" | Nonmetals	bgcolor="Template:Element color/Metalloids" | Metalloids	bgcolor="Template:Element color/Poor metals" | Poor metals	Atomic numbers in Template:Element color/Gas are gases	Atomic numbers in Template:Element color/Solid are solids	style="border:Template:Element frame/Primordial;" | Solid borders indicate primordial elements (older than the Earth)	style="border:Template:Element frame/Natural radio;" | Dashed borders indicate radioactive natural elements	style="border:Template:Element frame/Synthetic;" | Dotted borders indicate radioactive synthetic elements

Etymology

The name chalcogen comes from the Greek words χαλκος (chalkos, literally "copper"), and γενές (genes, born, gender, kindle). Thus the chalcogens bear copper. It was first used around 1930 by Wilhelm Biltz's group at the University of Hanover, where it was proposed by a man named Werner Fischer. Although the literal meanings of the Greek words imply that chalcogen means "copper-former", this is misleading because the chalcogens have nothing to do with copper in particular. "Ore-former" has been suggested as a better translation, wherefore both the vast majority of metal ores are chalcogenides and the word χαλκος in ancient Greek was associated with metals and metal-bearing rock in general; copper, and its alloy bronze, was one of the first metals to be used by humans.

Allotropes

Selenium is a chalcogen that has several allotropes. Two of them are the red allotrope and the black allotrope.

Occurrence

The first four chalcogens (O, S, Se, and Te) are all primordial on Earth. Polonium forms naturally after the decay of other elements, even though it is not primordial.

Production

Some isotopes of polonium are produced artificially, and all livermorium is produced artificially. These isotopes of polonium and livermorium are never found in nature.

Applications

Mining and Earth crustal composition explanation

In the Goldschmidt classification of elements, the chalcophile elements are Ag, As, Bi, Cd, Cu, Ga, Ge, Hg, In, Pb, Po, S, Sb, Se, Sn, Te, Tl, and Zn.

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

Chalcophile elements in this context are those metals (sometimes called "poor metals") and heavier nonmetals that have a low affinity for oxygen and prefer to bond with the heavier chalcogen sulfur as highly insoluble sulfides. (As noted in the introduction, chalcophile derives from Greek khalkós (χαλκός), meaning "ore" (it also meant "bronze" or "copper", but in this case "ore" is the relevant meaning), and is taken to mean "chalcogen-loving" by various sources).

Because these sulfides are much denser than the silicate minerals formed by lithophile elements, chalcophile elements separated below the lithophiles at the time of the first crystallisation of the Earth's crust. This has led to their depletion in the Earth's crust relative to their solar abundances, though because the minerals they form are nonmetallic, this depletion has not reached the levels found with siderophile elements.

In the Goldschmidt classification, the chalcophile elements are those shown in yellow. These include the chalcogens themselves, as they combine with each other. Additionally, gold may in some sense be considered a chalcophile, as most of the gold compounds found on Earth are gold chalcogenides (specifically gold tellurides). However, most gold on Earth is not found combined with any other element, but is found uncombined in alloys and fairly pure gold veins and metallic deposits.

Goldschmidt classification in the periodic table

	1	2		3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Group →
↓ Period
1	1 H																		2 He
2	3 Li	4 Be												5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg												13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca		21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr		39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba		71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra		103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cn	113 Nh	114 Fl	115 Mc	116 Lv	117 Ts	118 Og
				57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb
				89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No

Goldschmidt classification: Lithophile Siderophile Chalcophile Atmophile Trace/Synthetic

Biological role

Oxygen is needed by all animals. All animals need significant amounts of sulfur and trace amounts of selenium. Tellurium is not known to be needed for animal life, although a few fungi can incorporate it in compounds in place of selenium.

Toxicity

Chalcogens are generally non-toxic and in fact most of them are essential for life. The exceptions are polonium and livermorium; polonium is an extremely toxic and highly radioactive element, and too little livermorium has been synthesized to provide reliable information about its properties. Tellurium is also another example of a toxic chalcogen. It has no biological role and is slightly toxic. It is not nearly as toxic as polonium. However, exposure to high levels of oxygen, specifically at greater than normal barometric pressures can be toxic to the central nervous system (CNS). CNS oxygen toxicity is described as the "Paul Bert effect". Prolonged or very high oxygen concentrations can cause retinal damage in newborn and pre-term infants. There is a suspected link between Adult Respiratory Distress Syndrome and prolonged high level oxygen exposure. This may be due to oxidative damage to cell membranes, or absorption atelectasis, the collapse of the alveoli in the lungs. Also, while many of the chalcogens present little harm in their elemental form, some chalcogens are considerably toxic when they form compounds with other elements. For example, elemental sulfur is non-toxic although when it is burned in the presence of oxygen (found in air), it produces highly toxic fumes of sulfur dioxide. Hydrogen sulfide is also another example of an extremely toxic compound that includes a chalcogen. Hydrogen sulfide is also more toxic than sulfur dioxide however.

See also

• Gold chalcogenides