one model of ideal gases is that (a) they composed of particles so tiny compared to volume of the gas that they can be considered zero-volume point in space, and (b) there are interaction, attractive or repulsive, between the individual gas particles. However, real gas ultimately have behaviors due to the facts that (a) gas atoms and molecules do have a size, and (b) there is some interaction between the gas particles, which can range from minimal to very large. In considering the state variable of gas, the volume of the gas particles should have an effect on the volume V of the gas. the interaction between gas particles would have an effect on the pressure P of the gas. Perhaps a better equation of state for a gas should take these effect into account.
In 1873, the Dutch physicist Johannes van der Waals suggested a somewhat corrected version of the ideal gas law.