Band theory of solids

The band theory of solids explains how electrons behave in materials like metals, semiconductors, and insulators. In these materials, electrons occupy energy levels that form continuous ranges called bands. When bands overlap or are partially filled, electrons can move freely, making the material conductive (like metals). If bands are full and separated by gaps, electrons can't move easily, and the material acts as an insulator or semiconductor. This theory helps us understand why some materials conduct electricity better than others and is fundamental to designing electronic devices.