The Drude model was the first attempt to use the idea of a
'gas' of electrons, free to move between positively charged ionic
cores
Some assumptions were that electron collisions were
instantaneous and results in change in velocity and achieve thermal
equilibrium only through these collisions.
electrons were treated as free particles moving in a constant
potential.
Applied maxwell boltzmann statistics
Electrons were identical and distinguishable
Drude - Sommerfield model -
It was same as drude model with few modifications like it
treats electrons with Fermi - Dirac statistics
It treats electrons like particle in a box with constant
energy.
It makes use of pauli principle in order to distribute
electrons as per available energy states.