Posted by Ankur on Friday, January 11, 2013 at 8:53am.
xplain why the value of the band gap energy, Eg, decreases in the following homologous series:
Cdiamond=5.4 eV; Si=1.1 eV; Ge=0.72eV; Sn=0.08 eV.
As we move down the group, bond strength increases. As the strength increases, materials become more metallic in nature, since metals are strong. Metals tend to conduct electrons more easily, hence the band gap must decrease as materials become more metallic in nature.
Bond strength increases as we move down a group in the periodic table. The increasing bond strength tightens the spread between the valence and conduction bands, which in turn lowers the band gap of the material and allows it to be more conductive.
Due to the increasing nuclear mass, the bond strength decreases as we go down the group in the periodic table, and the resulting bonds within the material are weaker, meaning they require less energy to remove electrons, leading to a smaller band gap.
Due to the increasing atomic radius, valence electrons are more weakly bound, therefore the bond strength decreases as we go down the group in the periodic table, and the resulting bonds within the material are weaker, meaning they require less energy to remove electrons, leading to a smaller band gap.
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