The Chemistry Tutor: Learning by Example DVD Series provides an introduction to chemistry through step-by-step example problems. Emphasis is placed on giving students confidence in their skills by gradual repetition so that the skills learned are committed to long term memory. This episode covers atomic numbers, mass numbers, and isotopes, including the structure of the atom and how the atomic number is used to organize the periodic table. Grades 9-Adult. 34 minutes on DVD.