SG 041: Katharsis (STAR GATE - das Original) (German Edition)

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The lighter chalcogens, such as oxygen and sulfur, are rarely toxic and usually helpful in their pure form. Sulfur has more than 20 allotropes, oxygen has nine, selenium has at least five, polonium has two, and only one crystal structure of tellurium has so far been discovered. There are numerous organic chalcogen compounds. Not counting oxygen, organic sulfur compounds are generally the most common, followed by organic selenium compounds and organic tellurium compounds.

This trend also occurs with chalcogen pnictides and compounds containing chalcogens and carbon group elements. Oxygen is generally obtained by separation of air into nitrogen and oxygen. Sulfur is extracted from oil and natural gas. Selenium and tellurium are produced as byproducts of copper refining. Polonium and livermorium are most available in particle accelerators. The primary use of elemental oxygen is in steelmaking. Sulfur is mostly converted into sulfuric acid , which is heavily used in the chemical industry. Tellurium compounds are mostly used in optical disks, electronic devices, and solar cells.

Some of polonium's applications are due to its radioactivity. Chalcogens show similar patterns in electron configuration , especially in the outermost shells , where they all have the same number of valence electrons , resulting in similar trends in chemical behavior:. All chalcogens have six valence electrons. All of the solid, stable chalcogens are soft [8] and do not conduct heat well.

Density, melting and boiling points, and atomic and ionic radii [9] tend to increase towards the chalcogens with higher atomic numbers.

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Out of the six known chalcogens, one oxygen has an atomic number equal to a nuclear magic number , which means that their atomic nuclei tend to have increased stability towards radioactive decay. Sulfur has four stable isotopes, 20 radioactive ones, and one isomer. Selenium has six observationally stable or nearly stable isotopes, 26 radioactive isotopes, and 9 isomers. Tellurium has eight stable or nearly stable isotopes, 31 unstable ones, and 17 isomers. Polonium has 42 isotopes, none of which are stable. Livermorium isotopes through have been discovered.

The most stable livermorium isotope is Lv, which has a half-life of 0. The middle chalcogens selenium and tellurium have similar decay tendencies as the lighter chalcogens, but their isotopes do not undergo proton emission and some of the most neutron-starved isotopes of tellurium undergo alpha decay. Polonium's isotopes tend to decay with alpha or beta decay.

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Oxygen's most common allotrope is diatomic oxygen, or O 2 , a reactive paramagnetic molecule that is ubiquitous to aerobic organisms and has a blue color in its liquid state. Another allotrope is O 3 , or ozone , which is three oxygen atoms bonded together in a bent formation.

There is also an allotrope called tetraoxygen , or O 4 , [16] and six allotropes of solid oxygen including "red oxygen", which has the formula O 8. Sulfur has over 20 known allotropes, which is more than any other element except carbon. Other notable sulfur allotropes include rhombic sulfur and monoclinic sulfur. Rhombic sulfur is the more stable of the two allotropes.

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Monoclinic sulfur takes the form of long needles and is formed when liquid sulfur is cooled to slightly below its melting point. Gaseous sulfur is a mixture of diatomic sulfur S 2 and 8-atom rings. Selenium has at least five known allotropes. The gray allotrope of selenium is soft, with a Mohs hardness of 2, and brittle. The four other allotropes of selenium are metastable. These include two monoclinic red allotropes and two amorphous allotropes, one of which is red and one of which is black.

The gray allotrope of selenium is made from spirals on selenium atoms, while one of the red allotropes is made of stacks of selenium rings Se 8.

Tellurium is not known to have any allotropes, [21] although its typical form is hexagonal. The chalcogens have varying crystal structures. Oxygen's crystal structure is monoclinic , sulfur's is orthorhombic , selenium and tellurium have the hexagonal crystal structure, while polonium has a cubic crystal structure.

Oxygen, sulfur, and selenium are nonmetals , and tellurium is a metalloid , meaning that its chemical properties are between those of a metal and those of a nonmetal. Some sources refer to polonium as a metalloid, [1] [23] although it has some metallic properties. Also, some allotropes of selenium display characteristics of a metalloid, [24] even though selenium is usually considered a nonmetal.

Even though oxygen is a chalcogen, its chemical properties are different from those of other chalcogens.

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One reason for this is that the heavier chalcogens have vacant d-orbitals. Oxygen's electronegativity is also much higher than those of the other chalcogens. This makes oxygen's electric polarizability several times lower than those of the other chalcogens. For covalent bonding a chalcogen may accept two electrons according to the octet rule , leaving two lone pairs.

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Double bonds are also common in chalcogen compounds, for example in chalcogenates see below. Oxygen is the most electronegative element except for fluorine , and forms compounds with almost all of the chemical elements, including some of the noble gases. It commonly bonds with many metals and metalloids to form oxides , including iron oxide , titanium oxide , and silicon oxide.


Organic oxygen compounds are ubiquitous in organic chemistry. Sulfur-containing analogs of oxygen compounds often have the prefix thio-. Sulfur's chemistry is similar to oxygen's, in many ways. One difference is that sulfur-sulfur double bonds are far weaker than oxygen-oxygen double bonds, but sulfur-sulfur single bonds are stronger than oxygen-oxygen single bonds. Selenium, like most chalcogens, bonds with oxygen. There are many acids containing chalcogens, including sulfuric acid, sulfurous acid , selenic acid , and telluric acid.

All hydrogen chalcogenides are toxic except for water. For example, pyrite FeS 2 is an iron ore , and the rare mineral calaverite is the ditelluride Au , Ag Te 2. Although all group 16 elements of the periodic table, including oxygen, can be 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. Except for polonium, the chalcogens are all fairly similar to each other chemically. Sulfide minerals and analogous compounds produce gases upon reaction with oxygen. Chalcogens also form compounds with halogens known as chalcohalides.

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Such compounds are known as chalcogen halides. However, more complicated chalcogen halides, such as sulfenyl, sulfonyl, and sulfuryl halides, are less well known to science. Out of the compounds consisting purely of chalcogens and halogens, there are a total of 13 chalcogen fluorides, nine chalcogen chlorides, eight chalcogen bromides, and six chalcogen iodides that are known. Sulfur fluorides with low valences are fairly unstable and little is known about their properties. Sulfur tetrafluoride is also a well-known sulfur fluoride. Certain selenium fluorides, such as selenium difluoride , have been produced in small amounts.

The crystal structures of both selenium tetrafluoride and tellurium tetrafluoride are known. Chalcogen chlorides and bromides have also been explored. In particular, selenium dichloride and sulfur dichloride can react to form organic selenium compounds. Dichalcogen dihalides, such as Se 2 Cl 2 also are known to exist. There are also mixed chalcogen-halogen compounds.


These include SeSX, with X being chlorine or bromine. These compounds have been fairly recently structurally characterized, as of In general, diselenium and disulfur chlorides and bromides are useful chemical reagents. Chalcogen halides with attached metal atoms are soluble in organic solutions.