This document contains chemistry notes for secondary school students studying O-Level pure chemistry. It covers topics like measurements and units, separation techniques, collection of gases, purity of substances, tests for cations and anions, kinetic particle theory including the three states of matter, melting and freezing, boiling and condensation, sublimation, diffusion, atomic structure including atomic symbols and electron configuration. Diagrams and tables are provided to illustrate concepts. Key points are highlighted for each topic.