In this interactive PowerPoint presentation created by PJ Creek, atomic numbers and atomic masses are investigated. The lesson asks the question: "How do I figure out the number of protons, electrons, and neutrons in an atom?" The presentation focuses on how to calculate the number of each subatomic particle in an atom of an element when given data from the periodic table. For example, the element lithium is used to show that an atom of lithium has three protons, three electrons, and four neutrons. The elements magnesium and mercury are also used in this presentation.