Energy band gap is the energy difference between conduction band and valence band, i. e., energy required to an electron to overcome the energy levels between conduction band and valence band. In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also. A large number of free electrons thus, available are conduction electrons. The energy level of these electrons corresponds to the conduction level, hence valance level and conduction level are overlapped. Due to this, there is no gap between conduction band and valence band hence, for metals their separation is of the order of 0 eV.