The following diagrams show the electron populations of the bands of MO energy levels for four different materials:

. (c) Tell whether the conductivity of each material increases or decreases when the temperature increases.

Molecular Orbital (MO) Theory describes the behavior of electrons in molecules by combining atomic orbitals to form molecular orbitals. These orbitals can be filled with electrons and are categorized as bonding or antibonding. The arrangement of these orbitals influences the electrical properties of materials, including their conductivity.

The conductivity of materials is often affected by temperature changes. In semiconductors, increasing temperature typically provides energy to electrons, allowing them to move from the valence band to the conduction band, thus increasing conductivity. Conversely, in some metals, increased temperature can lead to increased lattice vibrations, which may decrease conductivity.

The band gap is the energy difference between the valence band and the conduction band in a material. Materials with a small band gap, like semiconductors, can have their conductivity significantly affected by temperature, as thermal energy can promote electrons across the gap. In contrast, materials with a large band gap are generally insulators and show little change in conductivity with temperature.