Aristotle felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that matter.
460
Democritus First proposed the existence of an ultimate particle. Used the word "atomos" to describe this particle.
Period: 460 to
Atom Timeline
John Dalton Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
Henri Becquerel while studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.
JJ Thomson discovers electron
Marie and Pierre Curie Studied radioactivity which turned out to be the spontaneous splitting of unstable atoms.
Robert Millikan discoverd that the elcectron is negatively charged
Ernest Rutherford established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
Niels Bohr: Bohr Model, The correct theory of the atom is called quantum mechanics; the Bohr Model is an approximation to quantum mechanics that has the virtue of being much simpler.
Louis de Broglie suggested that an electron moves with a wavelength that completes a circle, which would explain the different energy levels as Bohr’s model did but would also explain the wave diffraction pattern
James Chadwick discovered a previously unknown particle in the atomic nucleus. This particle became known as the neutron because of its lack of electric charge