sentences:  Space-filling calotte models are also referred to as CPK models after the chemists Robert Corey, Linus Pauling, and Walter Koltun, who over a span of time developed the modeling concept into a useful form.They are distinguished from other 3D representations, such as the ball-and-stick and skeletal models, by the use of the "full size" space-filling spheres for the atoms.They are useful for visualizing the effective shape and relative dimensions of the molecule, and the shapes of surface a given static conformer might present.