Group 14 hydrides arechemical compounds composed ofhydrogen atoms andgroup 14 atoms (the elements of group 14 arecarbon,silicon,germanium,tin,lead andflerovium).
The tetrahydride series has the chemical formulaXH4, with X representing any of the carbon family. Methane is commonly the result of the decomposition of organic matter and is agreenhouse gas. The other hydrides are generally unstable, poisonousmetal hydrides.
They take on a pyramidal structure, and as such are not polar molecules like the otherp-block hydrides.
Unlike other light hydrides such asammonia,water andhydrogen fluoride, methane does not exhibit any anomalous effects attributed tohydrogen 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) | CH4 |  |  |
| silicon tetrahydride hydrogen silicide (silane) | SiH4 |  |  |
| germanium tetrahydride hydrogen germanide (germane) | GeH4 |  |  |
| tin tetrahydride hydrogen stannide (stannane) | SnH4 |  |  |
| lead tetrahydride hydrogen plumbide (plumbane) | PbH4 |  |  |
| flerovium tetrahydride hydrogen flerovide (flerovane) | FlH4 |
This series has the chemical formulaX2H6. Ethane is commonly found alongsidemethane innatural gas. The other hydrides of the chemical formulaX2H6 are less stable than the corresponding tetrahydridesXH4, and they are more and more less stable as X goes fromcarbon (ethaneC2H6 is stable) down tolead (orflerovium) in theperiodic table (diplumbanePb2H6 is unknown[1]).
| Compound | Chemical formula | Molecular geometry | Space-filling model |
|---|---|---|---|
| Ethane (dicarbon hexahydride) (dicarbane) | C2H6 |  |  |
| Disilane (disilicon hexahydride) | Si2H6 |  |  |
| Digermane (digermanium hexahydride) | Ge2H6 |  |  |
| Distannane (ditin hexahydride) | Sn2H6 |  |  |
| Diplumbane (dilead hexahydride) | Pb2H6 |  |  |
| Diflerovane (diflerovium hexahydride) | Fl2H6 |
All straight-chain saturated group 14 hydrides follow the formulaXnH2n+2, the same formula for thealkanes.
Many other group 14 hydrides are known.Carbon forms a huge variety ofhydrocarbons (among the simplest alkanes aremethaneCH4,ethaneC2H6,propaneC3H8,butaneC4H10,pentaneC5H12 andhexaneC6H14, with a wide range of uses. There is alsopolyethylene(CH2)n, wheren is very large, a stable hydrocarbon polymer, the most commonly producedplastic.[2] Hydrocarbons also includealkenes, which contain adouble bond between carbon atoms (e.g.ethyleneH2C=CH2),alkynes, which contain atriple bond between carbon atoms (e.g.acetyleneH−C≡C−H),cyclic and branched hydrocarbons (e.g.cyclohexaneC6H12,limoneneC10H16, which is a cyclic hydrocarbon with double bonds between carbon atoms, andneopentaneC(CH3)4, which is a branched hydrocarbon), as well asaromatic hydrocarbons such asbenzeneC6H6 andtolueneC6H5−CH3), whose study forms the core oforganic chemistry.[3]
Alongsidehydrogen, carbon can form compounds with the chemically similarhalogens, forminghaloalkanes. The simplest of this series, thehalomethanes, contain compounds such asdichloromethaneCH2Cl2,chloroformCHCl3 andiodoformCHI3. Other such important chemicals includevinyl chlorideH2C=CHCl, which is used in the production ofPVC.
The other group 14 elements have a lower tendency to catenate. Hydrosilicons (binary silicon-hydrogen compounds), asilicon analogs of hydrocarbons, such assilanesSinH2n+2 are known forn = 1–8, in which thermal stability decreasing asn increases (e.g.silaneSiH4 anddisilaneSi2H6), as arecyclosilanes (e.g.cyclopentasilaneSi5H10 andcyclohexasilaneSi6H12). They are very reactive,pyrophoric colourless gases or volatile liquids. Their volatility is intermediate between thealkanes and the germanes.[4]Unsaturated silanes, thesilenes andsilynes, have been characterized spectroscopically. The first members of each respectively aredisileneH2Si=SiH2 anddisilyneH−Si≡Si−H, the silicon analogues ofethylene andacetylene respectively.
The first five hydrogermaniumsGenH2n+2 are known and are fairly similar to the hydrosilicones,[5] e.g.germaneGeH4 anddigermaneGe2H6. They aregermanium analogues of alkanes.
StannaneSnH4, a strong reducing agent slowly decomposes at room temperature totin and hydrogen gas, and is decomposed by concentrated aqueous acids or alkalis;distannane,Sn2H6 is still more unstable, and longer hydrostannums (hydrotins) are unknown. Stannane and distannane are tin analogues of methane and ethane respectively.
PlumbanePbH4 is very poorly characterised and is only known in trace amounts: even at low temperatures, synthesis methods that yield the otherMH4 compounds fail to givePbH4. No other hydroplumbums (hydroleads) are known.[1] However, some substituted diplumbanes, with a general chemical formulaR3Pb−PbR3 are more stable, where the R groups areorganyl.
Compounds containing hydrogen and multiple group 14 elements are known, one of the most famous of these beingtetraethylleadPb(CH2CH3)4 which containscarbon andlead. The other examples aremethylsilaneH3C−SiH3 which contains carbon andsilicon,tris(trimethylsilyl)germanium hydride((CH3)3Si)3GeH which contain carbon, silicon andgermanium,silylgermane or germylsilaneH3Si−GeH3 which contains silicon and germanium, andhexaphenyldiplumbane(C6H5)3Pb−Pb(C6H5)3 which contains carbon and lead.[6]