Group 14 Hydride

Group 14 hydrides are chemical compounds composed of hydrogen atoms and group 14 atoms (the elements of group 14 are carbon, silicon, germanium, tin, lead and flerovium).

Tetrahydrides

The tetrahydride series has the chemical formula , with X representing any of the carbon family. Methane is commonly the result of the decomposition of organic matter and is a greenhouse gas. The other hydrides are generally unstable, poisonous metal hydrides.

They take on a pyramidal structure, and as such are not polar molecules like the other p-block hydrides.

Unlike other light hydrides such as ammonia, water and hydrogen fluoride, methane does not exhibit any anomalous effects attributed to hydrogen bonding, and so its properties conform well to the prevailing trend of heavier group 14 hydrides.

Hexahydrides

This series has the chemical formula . Ethane is commonly found alongside methane in natural gas. The other hydrides of the chemical formula are less stable than the corresponding tetrahydrides , and they are more and more less stable as X goes from carbon (ethane is stable) down to lead (or flerovium) in the periodic table (diplumbane is unknown).

Higher group 14 hydrides

All straight-chain saturated group 14 hydrides follow the formula , the same formula for the alkanes.

Many other group 14 hydrides are known. Carbon forms a huge variety of hydrocarbons (among the simplest alkanes are methane , ethane , propane , butane , pentane and hexane , with a wide range of uses. There is also polyethylene , where ''n'' is very large, a stable hydrocarbon polymer, the most commonly produced plastic.Whiteley, Kenneth S.; Heggs, T. Geoffrey; Koch, Hartmut; Mawer, Ralph L. and Immel, Wolfgang (2005) "Polyolefins" in ''Ullmann's Encyclopedia of Industrial Chemistry''. Wiley-VCH, Weinheim. . Hydrocarbons also include alkenes, which contain a double bond between carbon atoms (e.g. ethylene ), alkynes, which contain a triple bond between carbon atoms (e.g. acetylene ), cyclic and branched hydrocarbons (e.g. cyclohexane , limonene , which is a cyclic hydrocarbon with double bonds between carbon atoms, and neopentane , which is a branched hydrocarbon), as well as aromatic hydrocarbons such as benzene and toluene ), whose study forms the core of organic chemistry.Greenwood and Earnshaw, p. 301.

Alongside hydrogen, carbon can form compounds with the chemically similar halogens, forming haloalkanes. The simplest of this series, the halomethanes, contain compounds such as dichloromethane , chloroform and iodoform . Other such important chemicals include vinyl chloride , which is used in the production of PVC.

The other group 14 elements have a lower tendency to catenate. Hydrosilicons ( binary silicon-hydrogen compounds), a silicon analogs of hydrocarbons, such as silanes are known for ''n'' = 1–8, in which thermal stability decreasing as ''n'' increases (e.g. silane and disilane ), as are cyclosilanes (e.g. cyclopentasilane and cyclohexasilane ). They are very reactive, pyrophoric colourless gases or volatile liquids. Their volatility is intermediate between the alkanes and the germanes.Greenwood and Earnshaw, p. 337. Unsaturated silanes, the silenes and silynes, have been characterized spectroscopically. The first members of each respectively are disilene and disilyne , the silicon analogues of ethylene and acetylene respectively.

The first five hydrogermaniums are known and are fairly similar to the hydrosilicones,Greenwood and Earnshaw, p. 374. e.g. germane and digermane . They are germanium analogues of alkanes.

Stannane , a strong reducing agent slowly decomposes at room temperature to tin and hydrogen gas, and is decomposed by concentrated aqueous acids or alkalis; distannane, is still more unstable, and longer hydrostannums (hydrotins) are unknown. Stannane and distannane are tin analogues of methane and ethane respectively.

Plumbane is very poorly characterised and is only known in trace amounts: even at low temperatures, synthesis methods that yield the other compounds fail to give . No other hydroplumbums (hydroleads) are known.Greenwood and Earnshaw, p. 375. However, some substituted diplumbanes, with a general chemical formula are more stable, where the R groups are organyl.

Compounds containing hydrogen and multiple group 14 elements are known, one of the most famous of these being tetraethyllead which contains carbon and lead. The other examples are methylsilane which contains carbon and silicon, tris(trimethylsilyl)germanium hydride which contain carbon, silicon and germanium, silylgermane or germylsilane which contains silicon and germanium, and hexaphenyldiplumbane which contains carbon and lead.

See also

* Methylene
* Methylidyne
* Titanium(IV) hydride , a structural analog of the group 14 tetrahydrides
* Zirconium hydride , and others
* Zirconium(II) hydride
* Uranium(IV) hydride

References

Bibliography

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{{Hydrides by group

Hydrides
Hydrogen compounds