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300
Aristotle
300 BC
Aristotle believed that there were only four elemnts: fire, water, earth and emotions which contribute to the good and bad in the world. He also did not believe on the idea of atoms. Aristotle believed that if you break a piece of paper in half over and over again you will never get to a point at which you can' break it in half. -
Period: 300 to
Atomic Theory
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460
Democritus
460BC
Democritus developed the idea that if you break a piece of paper in half over and over again you will evnetually be left with a small particle which he called the atom. So Dempcritus formed the thoery of the atom. -
Antoine Lavoisier
In 1778 Lavoisier did many experiments with gases, he basically discovered oxygen and hydrogen. When some substances were burned he stated that their loss in mass was gas molecules escaping into the atmosphere.This led him to establish the Law of Conservation of Mass. -
John Dalton
In1803 after many years of researching atoms John Dalton published his Theory on atoms which stated;All elements are made up of tiny indivisible particles, known as atoms.Atoms of the same element are identical with respect to their weights.Atoms of different elements are different from each other and can be identified by their relative weights.Atoms can neither be divided into smaller particles nor destroyed He also expanded upon the idea of definite proportions and the Law of Multiple -
Robert Millikan
In 1909 Robert Millikan performed his famous oil-drop experiment and discovered the size of electrons and the carge of all atoms, which are neutral. -
Henri Becquerel
Henri Becquerel discovered radioactivity along with Marie and Pierre Curie and also won the 1903 Nobel Physics Prize with them. He occupied the physics chair at the French Natural History Musuem. -
Marie & Pierre Curie
In 1896 Marie and Pierre Curie discovered two new radioactive elements: radium and polonium. It was for this new leap in physics that lead to them winning the Nobel Prize in Physics along with Marie's teacher Henri Becquerel. -
J.J Thomson
In 1897, the English physicist J.J. Thomson discovered the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and thought that matter must have a positive charge. His model looked like raisins stuck on the surface of a lump of pudding. This is called the plum-pudding model. -
Max Planck
Planck said that if you vibrate an atom enough the energy can be measured in certain units called quanta. This later lead to the discovery of the proton. -
Ernest Rutherford
Rutherford formed the Rutherford model of an atom and disproved the plum-pudding model saying that there was a nucleus and there was a almost impossible to see space in between the electrons and the nucleus. -
Niehls Bohr
Niehls Bohr came up with th idea that electrins move around in certain rings placed a certain disctance away from the nucleus. He disproved the idea that the electrons spiral into the nucleus. -
Henry Moseley
Moseley discovered a way to use X-rays to study the sturcture of atoms. He used this to make the Periodic Table more accurate. He was a student of Ruherford -
Erwin Schrodinger
In 1926 the Austrian physicist, Erwin Schrödinger effectively perfected the Bohr model by figuring out an equation that gave the energy levels of atoms. -
James Chadwick
Chadwick discovered the neutron. He realized that since the postive protons don't repel there has to be a neutral particle that holds them together in the nucleus. He called this the nucleus. -
Werener Heisenberg
In 1932, Heisenberg theorized that protons and electrons exchnge 'virutal' protons all the time at a very high speed. He called them virutal protons because no one can see them so no one can measure them. He also thoerized that it is impossible to tell the exact location of a subatomic prticle because they have so much energy.
