This lecture covers the historical development of atomic theory, starting from the early chemists to the modern quantum theory. It discusses the limitations of the Bohr model, the wave-particle duality of light and matter, and key breakthroughs by Einstein, Bohr, and de Broglie. The lecture delves into atomic emission spectra, blackbody radiation, the photoelectric effect, and the Schrödinger equation, explaining the quantization of energy levels in atoms and the concept of orbitals.