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500
Leucippus and Democritus come up with the idea that all matter is composed of tiny particles
Their reasoning behind this was that if you cut something in half enough times, you will reach something that can't be cut any more. They named these particles a tomos, meaning indivisible. This was the beginning of the atomic theory. -
Antone Lavoisier proposed the law of conservation of mass
This law states that even if matter changes shape or form, its mass remains the same. This discovery contributed to our knowledge of the behavior of atoms. -
James Dalton
He determined that elements exist as discrete packets of matter. This discovery also gave us new insight on atoms behavior and led to the question why do they behave the way they do. -
Cathode Rays
Scientists began probing things using discharge tubes. From this, they were able to discover that there were negative charges in the electrode rays and in matter. -
Eugen Goldstein
He discovered that since there were also positive electrodes flowing in the tube, that meant that there were positive charges in all matter along with negative charges. -
J.J Thompson
He was able to estimate the mass of the rays of electricity flowing through the discharge tubes. He found out that they weren't really rays, but negatively charged particles. -
Earnest Rutherford
His experiment with alpha particles led to the discovery of the nucleus of atoms and the fact that most of the atom is empty space. Later on he recognized the presence of positively charged particles named protons.His recognition of protons, neutrons, and electrons contributed to the thought that atoms had a neutral charge. -
Niels Bohr
His study of others work before him led him to predict the most likely position of electrons in and atom. We use the Bohr model today even thought we know electrons don't make perfect orbitals around the nucleus. -
Werner Heisenberg
He and some other scientists and chemists of the time proposed the Quantum Theory. This stated that electrons weren't particles or waves but they had properties of both and neither. This is the most current theory dealing with atoms and it is a result of constant building on others work to discover new things, even the work of Leucippus and Democritus.