when did the development of atomic theory begin
History of chemistry Dalton also proposed a modern atomic theory in 1803 which stated that all matter was composed of small indivisible particles termed atoms, atoms of a given element possess unique characteristics and weight, and three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). In 1808, Dalton first published New System of Chemical Philosophy (1808-1827), in which he outlined the first modern scientific description of the atomic theory. This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities.
Ernest Rutherford Rutherford moved in 1907 to the Victoria University of Manchester (today University of Manchester) in the UK, where he and Thomas Royds proved that alpha radiation is helium nuclei.[6][7] Rutherford performed his most famous work after he became a Nobel laureate.[5] In 1911, although he could not prove that it was positive or negative,[8] he theorized that atoms have their charge concentrated in a very small nucleus,[9] and thereby pioneered the Rutherford model of the atom, through his discovery and interpretation of Rutherford scattering by the gold foil experiment of Hans Geiger and Ernest Marsden. He conducted research that led to the first "splitting" of the atom in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered (and named) the proton.[10]