Lead sulfide electronic properties

So, if both sodium and lead are defined as metals and chlorine and sulfur as nonmetals, why is sodium chloride so different from lead sulfide Something appears to be missing in our definition of a metal. It is true that metals tend to lose electrons to nonmetals in a chemical reaction, but that definition turns out to be so broad that it is not very useful. How, then, should a metal be defined The answer was arrived at years before the electronic structure of atoms was known. Simply put, metals are best defined by their common physical properties ... 

Photochemistry of Titanium Dioxide Colloids. Another semiconductor colloid used in our studies is titanium dioxide which has a band gap of 3.2 eV. As in the case of cadmium sulfide, excitation of aqueous suspensions of this particle leads to electron-hole pair separation which can be intercepted with suitable redox reagents. In the absence of externally added solutes, the photogenerated electron-hole pair recombines to give the starting material and the light energy is dissipated to the medium as heat. Two types of TiOj samples are used in this study. TiOj prepared at high temperature (80°C) which behaves very similarly to commercial samples, and TlOj prepared at low temperature (35°C) which has a particle size of 300 100 A radius and shows different properties. 

R Rossetti, R Hul, JM Gibson, LE Brus. Hybrid electronic properties between the molecular and solid state limits lead sulfide and silver halide crystallites. J Chem Phys 83 1406-1410, 1985. 

The interest in small, zeohte-entrapped semiconductor particles, e.g., metal sulfides, mainly stems from the occurrence of quantum confinement effects. These effects lead to pecuhar optical and electronic properties, which make the materials attractive for apphcations in optoelectronic devices. In recent years, these new aspects of zeohte chemistry have grown in importance and have become a substantial branch of the increasing research field of nano chemistry. 

The differences in antiwear properties of disulfides are related to their ability to be physisorbed about 100 to 1000 times faster than monosulfide on metal surfaces. The differences can be explained in terms of the lower energy needed for the formation of the same number of RS" ions from disulfides (Kajdas,1994). The exposed metal surface is extremely reactive to lubricant components, especially antiwear and extreme-pressure additives resulting the formation of a film on the contact surface. The reaction of emitted electrons of low energy (1 to 4 eV) with molecules of oil additives adsorbed on the friction surface may lead to formation of negative ions and negative ion radicals. The investigator (Kajdas, 1994 and 1985) pointed out the indispensability of the metal oxide film on the rubbing surface from the viewpoint of the theory of sulfide film formation. 

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