I am new to solid state physics, having been in computational chemistry (quantum mechanics) for the larger part of my career. Hence have a lot of newbie like questions that are not easily answered by google/wikipedia searching. 1)In viewing a 1-dimensional band gap diagram, crossing the Fermi line from from either the conducting to non conducting zone or vice versa, is indicative of a metallic substance. Is this correct? 2) In band gap diagrams where there is no crossing of the Fermi line/level, the band gap can still be calculated by measuring the energy difference between the closest approach of the bands in the conducting and non-conducting zones? 3) Are there generally accepted band gaps that one can say a system is either conducting/semiconducting/nonconducting? 4) If the Fermi level for a system changes from a positive value to a negative value, is it a reasonable conclusion that the the system with the lower Fermi level would be more likely to allow charge migration, i.e. a current flow? Any help and recommendations for an easily read primer are also greatly appreciated.