Final answer:
John Dalton first proposed the atomic theory around 1803, presenting it in 1804 to the Royal Institution. His work laid the foundation for modern chemistry and inspired future discoveries, even though some aspects of his theory have since been revised.
Step-by-step explanation:
John Dalton and the Atomic Theory
The atomic theory was first formally proposed by the English chemist John Dalton around 1803. This cornerstone of chemistry was derived from experimental evidence and was a significant step forward from the ancient Greek philosophical idea of indivisible atoms. Dalton's atomic theory laid out several principles, among which were the notions that elements are composed of atoms, and that all atoms of an element are identical in mass and properties. Dalton presented his atomic theory in 1804 during a lecture to the Royal Institution, laying the foundation for modern chemistry.
Although certain aspects of Dalton's original atomic theory have been proven to be incorrect, such as the indivisibility of atoms and the identical nature of all atoms of an element, his work was pivotal. It inspired further research into the structure of atoms, eventually leading to the discovery of subatomic particles and radioactivity. Dalton's theory paved the way for scientists like Amedeo Avogadro, Dmitri Mendeleev, and Ernest Rutherford, and it remains one of the central theories in chemistry, with only minor revisions.