Atomic theory explains how one kind of atom may differ from another and ultimately why substances have different properties.
Many students cling to a planetary model of the atom.
When discussing atomic models, mention the cloudlike or wavelike nature of electrons in more advanced models. Provide a matrix with column headings such as name, atomic number, mass number, symbol, number of protons, number of neutrons, and number of electrons. Give the names, along with information in one or two of the squares, for every row of the matrix. Ask students to fill in the blanks. Provide information on proportions of isotopes of an element and their masses and have students determine the element's atomic mass.