The atomic theory of matter was first proposed by

The atomic theory of matter was first proposed as a scientific theory by the English chemist John Dalton in the early 19th century (specifically 1803 or 1808). While ancient philosophers like Democritus theorized about atoms, Dalton's model was the first based on experimental evidence and chemical laws, such as the law of conservation of mass and definite proportions. His theory posited that all matter is composed of tiny, indivisible particles called atoms. Subsequent scientists refined this model: J.J. Thomson discovered the electron in 1897, Ernest Rutherford proposed the nuclear model in 1911 after his gold foil experiment, and Niels Bohr introduced quantized energy levels in 1913. Thus, Dalton is credited with the first formal atomic theory of matter.