This is a brief kinesthetic exercise to help students try to understand atomic structure and ions better. Before class make up large signs that students can wear around their necks. A desk-top publisher can make this job easier and you can add some sort of cute pictures to go along with the text on the signs. You can start out simply with the hydrogen atom: one sign with "proton," one or two with "neutron," and one with "electron." Be sure to include the electrostatic charge of each particle. Have one member of the class wear each sign and invite them to come to the front of the room. Start with the most common isotope of hydrogen by having the proton stand in one place and the electron "orbit" the proton. Ask them what the net charge of the atom is. Add the neutron(s) and ask if the charge has changed. You can "ionize" by removing the electron. This whole thing may seem laughably simple-minded but you have to remember that many times you are dealing with learners in an early stage of college work. A great many Freshman biology students have had little experience in thinking abstractly. Therefore, kinesthetic exercises are appropriate. As the students spend more time thinking scientifically, they will come to need exercises such as this less and less.
Molecular models: Students can be challenged to make space-filling simulations of amino acids or monosaccharides using modeling clay.
Reference: Creager, J. 1993. Basic Health Science Chemistry: A Review and Workbook. Dubuque, IA: WCB/McGraw-Hill.
Here's a website from the University of Umea with a lot of interesting chemical education resources: http://www.anachem.umu.se/eks/pointers.htm