This unit on atomic structure is one of 10 first year units produced by the Independent Learning Project for Advanced Chemistry (ILPAC). The unit consists of two levels. Level one focuses on the atomic nucleus. Level two focuses on the arrangement of extranuclear electrons, approaching atomic orbitals through both electron bombardment and spectra. Two experiments are included: the electron method for determining ionizing energy and a qualitative examination of spectra of some s-block elements using a hand spectroscope. Also included are exercises (with answers), pre- and post-tests, and in appendices, a historical perspective on the topic and additional exercises on calculating relative atomic mass from percentage abundance. Students completing this ILPAC unit assume a greater responsibility for their own learning and can work, to some extent, at their own pace. By providing guidance, and detailed solutions to exercises in the units, supported by the optional use of video-cassettes, the project allows students to study A-level chemistry with less teacher contact time than a conventional course demands. (JN)