Electron Energy Band(电子能 带) energy b Energy band gapl Individual allowed energy states 个原子的情况 平闻距 Interatomic separation(原子间距) 代衰:一价金属(惘) 代表:二价金属(镁) 绝缘体 半导体 上mpty Empty Empty Emp conduction band Band gap Band gap Empty sta Filled Filled Filled states Band gap < 2ev excitation Electron valence2 2s Electron state 1s Electron state Electron Energy Band (电子能 带） 2sElectron energy band (12 states) 1sElectron energy band (12 states) Energy Individual allowed energy states Interatomic separation（原子间距） 12个原子的情况 原子间距 Energy band Energy band gap Energy band Energy Energy 平衡间距 Empty band (b) (a) Ef Ef Filled states Empty states Band gap Empty band Filled band 代表：一价金属（铜） 代表：二价金属（镁） Empty conduction band Empty conduction band Band gap Band gap Filled valence band Filled valence band (d) (c) Band gap > 2eV Band gap < 2eV 绝缘体 半导体 ∆Ef Energy Filled states Empty states Electron excitation ∆Ef Free Electron ∆E Eg Energy Conduction band Valence band Band gap Hole in valence band Electron excitation