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500 BCE
The Alchemists (500 BC)
The Alchemists did experiments trying to turn items into gold. One Alchemist, Leucippus, said that matter is made up of small particles that are always in motion. (healthresearchfunding.org) -
440 BCE
Democritus Comes up with Atom (440 BC)
Democritus is credited for being the first to come up with the atom. He believed that if you broke something down enough, it would become unbreakable. He also believed that matter could not be destroyed or created, and that different matter was just different groups and combinations of atoms. (sidmartinbio.org) -
430 BCE
Plato (430 BC)
Plato said that atoms were shaped in a few different ways. The ways he described were like that of a cube and other simple three dimensional figures, depending on the original shape of the matter. -
Robert Boyle (1660)
Robert Boyle contributed to ending the "four elements". He helped define an element (anything that can't be broken down into two or more things) and created Boyle's Law. -
Antone Lavoisier (1772)
Antone Lavoisier established the Law of Conservation of Mass. He also tried to get people to adopt the metric system of measurement. -
John Dalton (1803)
John Dalton said that natter can be broken down into atoms. He also said that different elements were just atoms with a different mass. He also thought how compounds were different combinations of atoms. (treehozz.com) -
Amadeo Avagadro (1815)
Amadeo Avagadro found Avagrado's Constant, which is used to calculate the results of chemical reactions. He also created Avagrado's law, which stated that two gases with the same temperature, pressure, and volume have an equal amount of molecules. -
Dmitri Mendeleev (1869)
Dmitri created the periodic table of elements. It would sort elements by their atomic weight. -
JJ Thomson (1900)
JJ Thomson was able to determine the mass to charge ratio for electrons. He knew that electrons were negatively charged. He came up with the Plum Pudding Model. -
Ernest Rutherford (1900)
Ernest Rutherford found that alpha particles could sometimes go through a thin sheet of gold foil, which caused a redesign of the atom. The new atom was "Electron Cloud" model. -
Albert Einstein (1905)
Albert Einstein created a mathematical formula for predicting the size of an atom and of molecules. He also stated that liquid molecules are in a constant state of motion, and that liquid is made up of atoms. -
Robert Millikan (1909)
Robert Millikan was credited for finding the value for the electron charge. -
Henry G. J. Moseley (1912)
Henry discovered that each element's identity is based on the number of protons the atom has. -
Neils Bohr (1913)
Neils Bohr proposed that the atom was made up of 3 particles, (the proton, neutron, electron) and where those particles were positioned in the atom. He also stated that electrons would orbit the nucleus at a fixed distance on a "energy level". Each energy level had a certain amount of electron particles it could carry. Each element would have a different number of electrons per energy level. -
Werner Heisenberg (1925)
Werner Heisenberg established the uncertainty principle, which states that a particle's position and movement can not be known exactly. -
Erwin Schrodinger (1926)
Schrodinger created a new mathematical formula to find the chance of finding an electron in a certain position. -
Pierre & Marie Curie (1930)
Marie Curie did a lot of research on radioactivity. She did an experiment on uranium rays and found that the rays remain constant, no matter what condition the uranium was in. She theorized that the rays originated in the uranium's atomic structure. -
James Chadwick (1932)
James Chadwick conducted an experiment where he shot Beryllium with alpha particles. He noticed that when this happened, the Beryllium would emit radiation. After he added paraffin wax, he concluded that the radiation was gamma rays. He found that the radiation was neutrally charged, meaning that the protons were being discharged. He found that the neutron had a heavier mass that the proton.