This document provides information about atoms and molecules: 1) It summarizes Dalton's atomic theory which states that matter is made of tiny indivisible particles called atoms that combine in small whole number ratios to form compounds. 2) It describes that an atom is the smallest particle of an element that retains chemical properties, and molecules are groups of atoms that are bonded together. 3) Key terms like atomic mass, molecular mass, ions, and the mole concept are explained which relate the mass of substances to the number of atoms or molecules.