A concept of the space occupied by an atom or ion permits students to understand clearly changes in chemical behavior as related to atomic or ionic size. Students see that atomic size decreases in any period as atomic number increases, and that atomic size in any group increases as atomic number increases. Change in size with change in charge also becomes apparent. Students are able to develop a better understanding of molecular shape, chemical bonds and crystal structure and what is meant by “close packing”. Colored spheres are used to illustrate relative radii of atoms and ions and to identify metallic (white), nonmetallic (blue) and amphoteric (shaded) elements. The chart is printed in three colors on heavy paper stock. Top and bottom edges are metal bound; top has metal tabs for hanging. This chart was originally designed by Professor J. A. Campbell, Oberlin College, Ohio. Size: 58" x 42".