- Characteristics of special compounds
- Carbonoids
- Nitrogenoids
- Nomenclature
- Training
- Carbonoids
- Nitrogenoids
- Applications
- References
The special compounds are all those made up of the covalent hydrides of the carbonoids and nitrogenoids. These are compounds with the formula EH 4, for the carbonids or group 14 elements, or the formula EH 3 for the nitrogenoids or group 15 elements.
The reason why some chemists refer to these hydrides as special compounds is not very clear; this name may be relative, although, ignoring that H 2 O is not found among them, some are very unstable and rare, so they could be worthy of such a qualifier.
Carboid and nitrogen hydrides. Source: Gabriel Bolívar.
Two hydride molecules EH 4 (left) and EH 3 (right) are shown in the upper image with a spheres and rods model. Note that EH 4 hydrides are tetrahedral, while EH 3 have trigonal pyramid geometry, with a pair of electrons above the central E atom.
As you go down groups 14 and 15, the central atom grows and the molecule becomes heavier and more unstable; since the EH bonds are weakened by the poor overlap of their orbitals. The heavier hydrides are perhaps the true special compounds, while CH 4, for example, is quite abundant in nature.
Characteristics of special compounds
By dividing the special compounds into two defined groups of covalent hydrides, a brief description of their characteristics will be given separately.
Carbonoids
As mentioned at the beginning, their formulas are EH 4 and consist of tetrahedral molecules. The simplest of these hydrides is CH 4, which is ironically also classified as a hydrocarbon. The most important thing about this molecule is the relative stability of its CH bonds.
Also, CC bonds are very strong, causing CH 4 to be concatenated to form the family of hydrocarbons. In this way, CC chains of great lengths and with many CH bonds arise.
Not the same with its heavier counterparts. SiH 4, for example, has very unstable Si-H bonds, which makes this gas a more reactive compound than hydrogen itself. Furthermore, their concatenations are not very efficient or stable, originating Si-Si chains of only ten atoms at most.
Among such concatenation products are the hexahydrides, E 2 H 6: C 2 H 6 (ethane), Si 2 H 6 (disilane), Ge 2 H 6 (digestman), and Sn 2 H 6 (diestannan).
The other hydrides: GeH 4, SnH 4 and PbH 4 are even more unstable and explosive gases, of which their reducing action is taken advantage of. PbH 4 is considered a theoretical compound, since it is so reactive that it could not be obtained properly.
Nitrogenoids
On the side of nitrogen hydrides or group 15, we find the trigonal pyramid molecules EH 3. These compounds are also gaseous, unstable, colorless, and toxic; but more versatile and useful than EH 4.
For example, NH 3, the simplest of them, is one of the most industrially produced chemical compounds, and its unpleasant smell characterizes it very well. The PH 3 for its part smells like garlic and fish, and the AsH 3 smells like rotten eggs.
All EH 3 molecules are basic; but NH 3 is crowned in this characteristic, being the strongest base due to the higher electronegativity and electron density of nitrogen.
NH 3 can also be concatenated, as can CH 4, only to a much lesser degree; hydrazine, N 2 H 4 (H 2 N-NH 2), and triazane, N 3 H 5 (H 2 N-NH-NH 2), are examples of compounds caused by the concatenation of nitrogen.
Similarly, the hydrides PH 3 and AsH 3 concatenate to give rise to P 2 H 4 (H 2 P-PH 2), and As 2 H 4 (H 2 As-AsH 2), respectively.
Nomenclature
To name these special compounds, two nomenclatures are used most of the time: the traditional and the IUPAC. Below the hydrides EH 4 and EH 3 will be broken down with their respective formulas and names.
- CH 4: methane.
- SiH 4: silane.
- GeH 4: German.
- SnH 4: stannane.
- PbH 4: plumban.
- NH 3: ammonia (traditional), azano (IUPAC).
- PH 3: phosphine, phosphane.
- AsH 3: arsine, arsan.
- SbH 3: stibnite, stiban.
- BiH 3: bismutin, bismutane.
Of course, the systematic and stock nomenclatures can also be used. In the first, the number of hydrogen atoms is specified with the Greek prefixes di, tri, tetra, etc. The CH 4 would come to be called according to this nomenclature carbon tetrahydride. While according to the stock nomenclature, CH 4 would be called carbon (IV) hydride.
Training
Each of these special compounds presents multiple methods of preparation, whether on industrial scales, laboratory, and even in biological processes.
Carbonoids
Methane is formed by various biological phenomena where high pressures and temperatures fragment hydrocarbons of higher molecular masses.
It accumulates in huge pockets of gases in equilibrium with oil. Also, deep in the Arctic it remains encased in ice crystals called clathrates.
Silane is less abundant, and one of the many methods by which it is produced is represented by the following chemical equation:
6H 2 (g) + 3SiO 2 (g) + 4Al (s) → 3SiH 4 (g) + 2Al 2 O 3 (s)
Regarding GeH 4, it is synthesized at the laboratory level according to the following chemical equations:
Na 2 GeO 3 + NaBH 4 + H 2 O → GeH 4 + 2 NaOH + NaBO 2
And SnH 4 is formed when it reacts with KAlH 4 in a tetrahydrofuran (THF) medium.
Nitrogenoids
Ammonia, like CH 4, can form in nature, especially in outer space in the form of crystals. The main process by which NH 3 is obtained is through the Haber-Bosch process, represented by the following chemical equation:
3 H 2 (g) + N 2 (g) → 2 NH 3 (g)
The process involves the use of high temperatures and pressures, as well as catalysts to promote the formation of NH 3.
Phosphine is formed when white phosphorus is treated with potassium hydroxide:
3 KOH + P 4 + 3 H 2 O → 3 KH 2 PO 2 + PH 3
Arsine is formed when its metal arsenides react with acids, or when an arsenic salt is treated with sodium borohydride:
Na 3 As + 3 HBr → AsH 3 + 3 NaBr
4 AsCl 3 + 3 NaBH 4 → 4 AsH 3 + 3 NaCl + 3 BCl 3
And bismuthin when methylbismuthin is disproportionate:
3 BiH 2 CH 3 → 2 BiH 3 + Bi (CH 3) 3
Applications
Finally, some of the many uses of these special compounds are mentioned:
- Methane is a fossil fuel used as cooking gas.
- Silane is used in organic synthesis of organosilicon compounds by adding to the double bonds of alkenes and / or alkynes. Also, silicon can be deposited from it during semiconductor manufacturing.
- Like SiH 4, Germanic is also used to add Ge atoms as films in semiconductors. The same applies to stibine, adding Sb atoms on silicon surfaces by electrodeposition of its vapors.
- Hydrazine has been used as rocket fuel and to extract precious metals.
- Ammonia is destined for the fertilizer and pharmaceutical industry. It is practically a reactive source of nitrogen, allowing the addition of N atoms to countless compounds (amination).
- Arsine was considered a chemical weapon during World War II, leaving the infamous phosgene gas, COCl 2, in its place.
References
- Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
- Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
- Chemistry. (2016, April 30). Special compounds. Recovered from: websterquimica.blogspot.com
- Alonso Formula. (2018). H with no metal. Recovered from: alonsoformula.com
- Wikipedia. (2019). Group 14 hydride. Recovered from: en.wikipedia.org
- The Chemistry guru. (sf). Hydrides of nitrogen. Recovered from: thechemistryguru.com