- Democritus, born around 460/470 BC, was the first to introduce the atomic theory and theorized that all materials are made up of indivisible 'atoms'
- John Dalton, in 1803, expanded on the theory, stating that all atoms of an element are the same and conducted experiments to support his speculations
- J.J. Thomson, in 1897, discovered the electron and proposed the plum pudding model of the atom
- Ernest Rutherford, in 1909, concluded that atoms have a positively charged nucleus and electrons orbit around it
- The atomic theory timeline shows the progression of our understanding of the atom from the earliest philosophies to the modern-day atomic model
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