Two common alltropes of carbon are dimond in which each atom form four alph bond

Question

Two common alltropes of carbon are dimond in which each atom form four alph bonds, and graphite in which each atoms forms three alpha bonds and on pi-bond.for elemental sillicon and germanium,the standard state are dimond like structures: the graphite-like lattice is unknown. Explain wo common allotropes of carbon are diamond in which each atom forms fo r bonds, and graphite in w ih each three bonds and one bond. For elemental siloon and germanium, the standard states are diamond atom forms like structures: the graphite-like lattice is unknown. Explain

Explanation / Answer

Damond is an insulator, but silicon is a semiconductor. This is because the band gap in Si is smaller than that in C.

There is no Si analogue of graphite; the larger size if the Si atom means that the overlap of the Si p-orbitals is poor, and hence that Si p-p bonding is poor.

Si forms strong bonds to more electronegative elements, eg. Si-F and Si-O, whereas C forms strong bonds with less electronegative elements, eg. C-H. Hydrocarbons are more stable than silicon hydrides both with respect to decomposition to the elements and combustion to the dioxide and water. Silane (SiH4) is also spontaneously flammable (it is labile) whereas methane requires sparking to burn (it is inert).

The amorphous form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, which is essentially graphite but not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal pressures carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons.[38] The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak van der Waals forces. This gives graphite its softness and its cleaving properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a -cloud, graphite conducts electricity, but only in the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.

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