Final answer:
John Dalton developed a modern atomic theory grounded in experimental evidence, unlike Democritus, whose ideas lacked empirical support. Dalton's theory was based on the law of definite proportions and provided a detailed explanation of chemical reactions.
Step-by-step explanation:
What did Dalton do that Democritus did not in developing his atomic theory? John Dalton, an English scientist, introduced a modern atomic theory based on experimental evidence, which was a significant advancement beyond the philosophical ideas of ancient Greek philosophers like Democritus. Democritus's ideas on atoms were purely speculative and lacked empirical support. In contrast, Dalton's atomic theory was formulated by focusing on experimental results such as the study of the weights of various elements and compounds, and the behavior of gases. Democritus had proposed that atoms were indivisible and differed only in shape, size, and mass. Dalton's theory went further, providing a detailed explanation of chemical reactions based on the weight ratios of elements. He observed that matter always combined in fixed ratios by weight or volume, supporting Proust's law of definite proportions. Dalton's theory was revolutionary as it laid the foundation for modern chemistry and was backed up by experimental evidence, making it far more concrete and accepted in the scientific community of his time.