The Zimbabwe Secondary School Science Project (ZIM-SCI) developed student study guides, corresponding teaching guides, and science kits for a low-cost science course which could be taught during the third year of secondary school without the aid of qualified teachers and conventional laboratories. This ZIM-SCI study guide is a four-part unit providing activities and experiments which build on concepts about particles learned in ZIM-SCI units C1 ("What is Water?") and C2 ("Particles in Action"). The material included expands students' knowledge to cover requirements of the O-Level General Science Syllabus. Part 1 focuses on elements, compounds, and mixtures, with references to basic concepts taught in units C1 and C2. Part 2 deals with particulate structure in matter with reference to Brownian motion. The concept of electrostatics is introduced in part 3 to get across the idea of matter being made up of tiny charged particles (ions). Protons and neutrons are also introduced. Part 4 deals with various aspects of chemical bonding. Actual O-level examination questions (with answers) as well as information on principles behind the activities and experiments are provided. (JN)