The postulates of atomic theory, first proposed by John Dalton in the early 19th century, state that all matter is composed of tiny, indivisible particles called atoms. Each element consists of identical atoms, which differ from those of other elements. Atoms can combine in simple whole-number ratios to form compounds, and chemical reactions involve the rearrangement of these atoms, not their creation or destruction. Later developments in atomic theory introduced modifications, such as the discovery of subatomic particles like protons, neutrons, and electrons. These findings showed that atoms are not indivisible but made up of smaller components, leading to a more complex understanding of matter and its interactions.