There are multiple ways of looking at the ideal gas model. One is to say we have point particles colliding elastically (as an ideal scenario) and proceed to obtain the exact equation of state, i.e $pV=nRT$. The other approach, is to state a priori the relevant length scales and time scales at which the system is going to be studied are sufficiently macroscopic, so as to be able to disregard any microscopic structure in the constituent particles. In both cases, the excluded volume effect (which is what the effect of existence of a finite size of particles in a gas is called) is neglected, as a model assumption in the first case and as a practical approximation in the second. The simplest fluid models that can be solved analytically are the so-called hard sphere models which involve the crudest form of binary excluded volume interactions. In such a case, one can in principle write down the entire virial equation for pressure (the virial coefficients being calculable from microscopic parameters of the model, size of the particles included) and hence the equation of state for this fluid is derivable. The Van der Waals equation is a specific mean field limit of such a virial expansion. The effect of excluded volume will be most prominent a low temperatures and high densities and it will have a substantial effect on the condensation of the fluid (the critical temperature and the scaling laws).