Trend 4.10 of the Carbon Group (Group IVA) Trends says that SiH4 hydrolyses in the presence of trace amounts of base more readily than CH4, GeH4, and SnH4.
Why?[]
SiH4 + 2H2O(aq) ----> SiO2(s) + 4H2(g)
SiH4 reacts more readily than other Group IVA elements for a combination of reasons.
One reason is that it has long bond lengths. Carbon has short bonds as a result of the Uniqueness Principle and therefore higher bond enthalpy and more stable bonds. This as well as kinetic inertness keeps CH4 from reacting as readily as SiH4 does.
There is another reason, however, because GeH4 has longer bonds as well, similar to SiH4, but it does not react as readily as SiH4 does. An additional factor is the redox reaction. Because of electronegativity values, in Si-H the H is hydric (-) wehre in Ge-H and C-H, the H is protic (+). Therefore in the SiH4 reaction there is redox occuring where H+ and H- come together to form H2 gas. The CH4 and GeH4 reactions do not have this added redox drive.
Silane importance[]
SiH4 is shown in red.
This gas is a very important compound; whereas the other hydrides in this group are generally not useful. This compound is stable in water itself, but adding base rapidly yields hydrolysis to create SiO2 and H2.[1]
Properties[]
- SiH4 is a colorless gas just as the other hydrides from the group are[1] - see figure for boiling point relative to other group IV hydrides in red
- Silane is the most important of the group IV hydrides[2]
- Silane is flammable[1]
Preparation[]
Prepare silane by reduction of SiCl4 with LiAlH4 in an ether. Another way to create it is by action of LiAlH4 on SiO2 at a high temperature. SiH4 is tetrahedral, as shown in the figure.[3]
Uses[]
The most important reaction including Si-H bonds is the hydrosilation reaction of alkenes which is as follows:
RCH=CH2 + SiHCl3 ---> RCH2CH2SiCl3
This reaction is so important because it is used in the process of forming silicones.
Another important reaction is the following. It makes silane (below in bold) that is very high purity, and is used semiconductor quality silicon3, which is especially useful in the electronics industry.
Si + 2 H2 + 3 SiCl4 → 4 SiHCl3 2 SiHCl3 → SiH2Cl2 + SiCl4
2 SiH2Cl2 → SiHCl3 + SiH3Cl
2 SiH3Cl → SiH4 + SiH2Cl2
References[]
- ↑ 1.0 1.1 1.2 Cotton, Albert. Wilkinson, Geoffrey. Basic Inorganic Chemistry. 3rd ed.
- ↑ http://www.vias.org/genchem/kinetic_12450_08.html
- ↑ http://en.wikipedia.org/wiki/Silane