Hydrogen Compounds Of Group Iv Elements

Man has known carbon, as charcoal from the combustion of wood, from prehistoric times. Its name derives from the Latin carbo meaning charcoal. The element is unique in the vast number of its compounds- there are probably more than one million known today. Carbon is widely distributed throughout the universe. Much of the energy of the sun and stars is due to the carbon cycle. Both black and transparent diamonds have been found in meteorites. The cosmic abundance is six times that of silicon.

The name of this element derives from a corruption of the Greek word adamas meaning invincible. Combined with hydrogen, carbon occurs extensively as coal, petroleum and natural gas. In spite of its wide spread occurrence carbon still only constitutes 0. 027% of the earth s crust. The distribution of terrestrial carbon is approximately as follows: minerals-99. 7%, atmosphere-0. 2%, and living matter-0. 01%. Even if combining with hydrogen is very difficult to achieve, a great number of hydrides of carbon is known which is the object of organic chemistry.

The hydrides of carbon are covalent compounds. Carbon possesses in the valence shell four electrons and forms four bonds in almost all of its combinations. The bonds of carbon aren t made with the pure orbitals 2s2p, but with some hybrid tetrahedral orbitals. The saturated hydrides of carbon don t have an acid character, which means that don t have the tendency to loose protons. In a period this tendency increases from the 4th to the 7th group. So in the series: H HF gives easily the proton to water and forms ions like F?

and H3O+. Ammonia and methane don t loose protons. The acid or basic properties of some combinations can be explained by the presence in its molecules of lone pairs, able to form coordinate bonds. The hydrides of carbon don t have lone pairs, so they are neutral. The tendency to form covalent bonds and the neutral character allows carbon atoms to bond between themselves and to form chains of various forms.

Regarding its health hazard carbon is itself relatively non-toxic. The radiological hazards of using radioactive carbon compounds have already been discovered. For 14C, the most widely used radioisotope, the tolerance doses are: Whole body burden 300uC Maximum permissible concentration in drinking water 8x10-3uC ml-1 Maximum permissible concentration in air 4x10-6uC ml-1 Silicon.

It is not possible to say when or by whom silicon and its early compounds were discovered, because man has used natural silica and silicates since dawn of the race. The name silica (and from it, the words silicon, silicide, silicate, and silicone by the usual etymology) comes from the Latin word silex, silicis for flint.

Silica was found to be a relatively strong acid earth at high temperature, capable of forming salts of all the alkali and alkaline-earth metals and of most transition metals as well. In this way some understanding of the ancient ceramic arts became ...

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