Atoms and Molecules
Chapter 3 of the Class 9 NCERT Science textbook builds chemistry from the laws of chemical combination. Dalton's atomic theory explains why elements unite in fixed ratios, and atoms, molecules and ions give names to the particles involved. Learners write chemical formulae using valency, work with atomic and molecular masses, and meet the mole as a counting unit for particles. The chapter turns abstract symbols into a precise language for describing every substance and the proportions in which substances react.
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