The macroscopic model of a particle as a sphere with an exactly determined surface is not adequate in the nanometer size range. Two various parameters are used to describe the size of a particle. The difference between the collision radius and the mass radius of a particle is estimated to be 0.115 nm fitting a new semiempirical model to the experimental data. Transition from the elastic collisions specific for molecules to the inelastic collisions specific for macroscopic particles is described using the Einstein factor of the ＇＇melting＇＇ of the particle internal energy levels. Dipol polarization interaction is included into the model using the (infinity - 4) potential. The model is approaching the Chapman-Enskog equation in the free molecule limit and the Millikan equation in the macroscopic limit. An algorithm is presented to calculate the particle mobility and diffusion coefficient according to the parameters of ambient gas and the particle.