Dalton's table of elements with his diagram of atoms, 1806-1807.
© Science Museum / Science & Society Picture Library
Dalton's table of elements showing symbols and atomic weights. Lying beside it is Dalton's diagram representing the atoms of elastic fluids (rolled up) and three atomic models. Reproductions produced in 1925 from the originals held by the Manchester Literary and Philosophical Society. John Dalton (1766-1844) formulated the atomic theory to explain chemical reactions, based on the concept that the atoms of different elements are distinguished by differences in their weights. This theory has influenced scientific thought for more than a century and a half.