Chemistry:Group 14 hydride

Short description: Type of chemical compound

Methane, silane, and germane, three simple group 14 hydrides

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 XH
4, 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.

Compound	Chemical formula	Molecular geometry	Space-filling model
carbon tetrahydride hydrogen carbide methane (carbane)	CH 4
silicon tetrahydride hydrogen silicide (silane)	SiH 4
germanium tetrahydride hydrogen germanide (germane)	GeH 4
tin tetrahydride hydrogen stannide (stannane)	SnH 4
lead tetrahydride hydrogen plumbide (plumbane)	PbH 4
flerovium tetrahydride hydrogen flerovide (flerovane)	FlH 4

Hexahydrides

This series has the chemical formula X
2H
6. Ethane is commonly found alongside methane in natural gas. The other hydrides of the chemical formula X
2H
6 are less stable than the corresponding tetrahydrides XH
4, and they are more and more less stable as X goes from carbon (ethane C
2H
6 is stable) down to lead (or flerovium) in the periodic table (diplumbane Pb
2H
6 is unknown).

Compound	Chemical formula	Molecular geometry	Space-filling model
Ethane (dicarbon hexahydride) (dicarbane)	C 2H 6
Disilane (disilicon hexahydride)	Si 2H 6
Digermane (digermanium hexahydride)	Ge 2H 6
Distannane (ditin hexahydride)	Sn 2H 6
Diplumbane (dilead hexahydride)	Pb 2H 6
Diflerovane (diflerovium hexahydride)	Fl 2H 6

Higher group 14 hydrides

All straight-chain saturated group 14 hydrides follow the formula X
nH
2n+2, the same formula for the alkanes.

Cubane, a Platonic hydrocarbon and prismane

Many other group 14 hydrides are known. Carbon forms a huge variety of hydrocarbons (among the simplest alkanes are methane CH
4, ethane C
2H
6, propane C
3H
8, butane C
4H
10, pentane C
5H
12 and hexane C
6H
14, with a wide range of uses. There is also polyethylene (CH
2)
n, where n is very large, a stable hydrocarbon polymer, the most commonly produced plastic. Hydrocarbons also include alkenes, which contain a double bond between carbon atoms (e.g. ethylene H
2C=CH
2), alkynes, which contain a triple bond between carbon atoms (e.g. acetylene H–C≡C–H), cyclic and branched hydrocarbons (e.g. cyclohexane C
6H
12, limonene C
10H
16, which is a cyclic hydrocarbon with double bonds between carbon atoms, and neopentane C(CH
3)
4, which is a branched hydrocarbon), as well as aromatic hydrocarbons such as benzene C
6H
6 and toluene C
6H
5–CH
3), whose study forms the core of organic chemistry.

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 CH
2Cl
2, chloroform CHCl
3 and iodoform CHI
3. Other such important chemicals include vinyl chloride H
2C=CHCl, 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 Si
nH
2n+2 are known for n = 1–8, in which thermal stability decreasing as n increases (e.g. silane SiH
4 and disilane Si
2H
6), as are cyclosilanes (e.g. cyclopentasilane Si
5H
10 and cyclohexasilane Si
6H
12). They are very reactive, pyrophoric colourless gases or volatile liquids. Their volatility is intermediate between the alkanes and the germanes. Unsaturated silanes, the silenes and silynes, have been characterized spectroscopically. The first members of each respectively are disilene H
2Si=SiH
2 and disilyne H–Si≡Si–H, the silicon analogues of ethylene and acetylene respectively.

The first five hydrogermaniums Ge
nH
2n+2 are known and are fairly similar to the hydrosilicones, e.g. germane GeH
4 and digermane Ge
2H
6. They are germanium analogues of alkanes.

Stannane SnH
4, a strong reducing agent slowly decomposes at room temperature to tin and hydrogen gas, and is decomposed by concentrated aqueous acids or alkalis; distannane, Sn
2H
6 is still more unstable, and longer hydrostannums (hydrotins) are unknown. Stannane and distannane are tin analogues of methane and ethane respectively.

Plumbane PbH
4 is very poorly characterised and is only known in trace amounts: even at low temperatures, synthesis methods that yield the other MH
4 compounds fail to give PbH
4. No other hydroplumbums (hydroleads) are known. However, some substituted diplumbanes, with a general chemical formula R
3Pb–PbR
3 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 Pb(CH
2CH
3)
4 which contains carbon and lead. The other examples are methylsilane H
3C–SiH
3 which contains carbon and silicon, tris(trimethylsilyl)germanium hydride ((CH
3)
3Si)
3GeH which contain carbon, silicon and germanium, silylgermane or germylsilane H
3Si–GeH
3 which contains silicon and germanium, and hexaphenyldiplumbane (C
6H
5)
3Pb–Pb(C
6H
5)
3 which contains carbon and lead.

See also

• Methylene CH
  2
• Methylidyne CH
• Titanium(IV) hydride TiH
  4, a structural analog of the group 14 tetrahydrides
• Zirconium hydride ZrH
  4, ZrH
  2 and others
• Zirconium(II) hydride ZrH
  2
• Uranium(IV) hydride UH
  4