Electrons undergo motion due to the effect of electrical and magnetic fields, or thermal energy. The motion of electrons under the effects of thermal kinetic energy lends them thermal velocity, whereas the motion of electrons under the effects of electrical or magnetic fields lends them drift velocity.
For electrons to be free to move in a material, special conditions regarding the electronic configuration of the material must be satisfied. The outer shells of the atoms comprising the material must be partially filled. These shells agglomerate to form semi-continuous bands. Materials with partially filled bands, such as metals and semiconductors at room temperature, allow delocalized electron motion, resulting in thermal and electric conduction.
Thermally induced motion in electrons is random, resulting in no net current being generated in any direction in an isothermal material. The motion of electrons with temperature depends on the type, inclusions and imperfections of the material. Generally, thermal velocity of electrons increases with increasing temperature. This increase may be linear or polynomial depending on the intrinsic and extrinsic material properties.
Electrons accelerate in an electric or magnetic field under the effects of the Columbic and Lorentz forces. This acceleration reaches a maximum value when the impurities and imperfections deflecting the electrons exert and equal and opposite force to the accelerating field.