Conductor, semiconductor and insulator
*) The electrons are filled in shells according to formula 2n^2, where (n) is the number of shell. The outermost shell can shell can have maximum of 8 electrons. The electrons present in the outer most shell belongs to valance band or valance energy band , the outermost band of atom. The electrons present in the outermost shell have maximum energy and as we move closer to nucleus the energy of electrons in coming shells keep on decreasing, that is the reason why the e in the innermost shell are strongly bound to the nucleus. Suppose a sheet of metal, having millions of atoms. And if we give energy to electrons, than that e's detaches from their parent atoms but moves freely within that sheet, now the band in which they move is called as conduction band or conduction energy band . In conduction band e moves as free charge carrier. The energy can be given as thermal energy or by applying voltage. after loosing energy it again falls into valance band. *) Insulator , forbidden ...