History & Development of the Atomic Model
Dalton's "Billiard Ball" Model (1803) was the first proper atomic theory that you'd recognise today. He imagined atoms as solid, indivisible spheres - a bit like tiny snooker balls bouncing around. Dalton also figured out that all atoms of the same element are identical, and that atoms can't be created or destroyed in chemical reactions.
Thomson's "Plum Pudding" Model (1897) came after Thomson discovered electrons using cathode ray tubes. He pictured the atom as a sphere of positive charge with negatively charged electrons dotted throughout it - like raisins in a Christmas pudding. The positive matter was thought to be thick and jelly-like, whilst the electrons could move around within it.
Rutherford's Nuclear Model completely revolutionised atomic theory after his famous alpha particle scattering experiment. He discovered that most of an atom's mass is packed into a tiny central nucleus, with the rest being mostly empty space. This was shocking because it meant atoms are mostly nothing!
Bohr's Model (1913) refined Rutherford's ideas by proposing that electrons orbit the nucleus in fixed circular paths called shells. Each shell has a specific energy level and can only hold a maximum number of electrons. Finally, in 1932, Chadwick discovered neutrons, completing our understanding that the nucleus contains both protons and neutrons.
Quick Tip: Remember the timeline - each model built on the previous one's discoveries, fixing problems and adding new particles as technology improved!