Hi, Iam trying to understand the differences between metals, semiconductors and insulators. Regarding the conductivity properties. Iam new to this area so please correct me if Im wrong. I may be simplifying things now; 1) If I put a voltage over a solid, I only measure a current if there are empty energy states for the electrons to occupy with their available energy (thermal or whatever). 2) The reason why metals conduct electricity so good is because there are empty (higher) energy states. And the reason for that, is because when these atoms bind into a solid, they bond in such way that the electron configuration leaves some available states in the sub shells, e.g. s- or p-sub shells are not full. 3) Semiconductors and insulators bond in such way that all states are full. However, the differences between semi and insulators is the band gap, and Iam not really sure what determines this, the magnitude of the bandgap. Maybe something with cosinus function, K values and Schrödinger equation? If Im right in this (2), why (or what makes them not to) does metal not bond in covalent bonds in such way that all states are full, like in insulators. Thank you very much for your time!