Silicon
Elementary silicon is a bluish/black solid which can be
smooth like a mirror. It is a semiconductor and as such is used in all modern
electronics. Elementary silicon probably is produced at the highest purity of
all known compounds. Commercial samples of silicon, used in the semiconductor
industry can have purities of 99.9999% or better. Silicon is quite inert, though
not as inert as boron. It is attacked by alkaline solutions, producing hydrogen
gas and silicate in solution. Acids do not have a strong effect on silicon.
Elementary silicon only is of limited interest for the average home lab. It is
not very reactive at room temperature. It can, however, be purchased through eBay from chemical elements-collector
items suppliers at reasonable price, sometimes in the form of nice shiny wafers,
sometimes in the form of crystalline chunks.
Silicon has the +4 oxidation state in its compounds with oxygen. It has oxidation state -4 to 0 in its compounds with hydrogen.
Silicon is part of many rock-like compounds on earth. Silicon dioxide is the
main constituent of ordinary white sand. Quartz crystals are almost pure silicon
dioxide. Many other minerals also contain silicon in the form of orthosilicates,
containing SiO44-, or containing complex chains of formula
(SiO32-)n, outbalanced with a certain metallic
cation. These rocky minerals all are highly insoluble. For the home chemist,
silicate is not the most interesting compound. Only a few silicates are soluble
in water. Silicate chemistry becomes much more interesting at high temperatures
(1000+ °C), but this is out of reach of the average home chemist.
The only soluble silicate compound, available for the public, is Na2SiO3. This is sold as a strong solution in water, called waterglass.
Waterglass can be used for a funny experiment, called chemical garden. Adding crystals of soluble colored metal salts (e.g. copper sulfate, ferric sulfate, nickel sulfate) to a 10% solution of sodium silicate yields all kinds of "underwater-vegetation", due to osmotic processes and formation of precipitates.
Silicon also forms a class of compounds, analogous to the carbon-alkanes. These
silicon compounds have generic formula SinH2n+2 and are
called silanes. Where the series of carbon-alkanes can go up almost without
limit for n, for silicon n is limited to small integer values. The most stable
silane is SiH4. Silanes, being gases or low-boiling liquids, however,
are not suitable for home chemistry. Handling them is extremely difficult,
because they inflame, as soon as they come in contact with air.