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460 BCE
Democritus was born
Democritus expanded the Atomic Theory to state that matter was composed of small particles called "atoms" that could be divided no further. These atoms were all composed of the same primary matter with the only differences between them being their size, shape, mass, positions and arrangement. The differences in these characteristics explained the differences in the properties of the matter around us. -
442 BCE
The First Atomic Model was created, The Democritus Model
Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogeneous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them. -
370 BCE
Democritus died
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John Dalton was born
John Dalton investigated into the great depths of chemistry. He came up with a theory on the smallest particles in the universe, of what makes up what we call "matter". All matter consists of indivisible particles. Dalton gave the name to these minute particles, the atom.There are different types of atoms, these are called elements. Each of these elements is different from one another only by its weight. Atoms of the same element all have the same mass. -
The Billiard Ball Model was created
This model looked the same Democritus's model, and it was put forth in 1803 but no one knew the exact date. It says February the 3rd because there is no way to just leave it at 1803 by itself. -
J.J. (Joseph John) Thomson was born
J.J. Thomson was an English scientist. He discovered the electron when he was experimenting with gas discharge tubes. He noticed a movement in a tube.He called the movement cathode rays.The rays moved from the negative end of the tube to the positive end.He realized that the rays were made of negatively charged particles and called it electrons. -
Lord Ernest Rutherford was born
Ernest Rutherford conducted a famous experiment called the gold foil experiment. He took a thin sheet of gold foil. He used special equipment to shoot alpha particles (positively charged particles) at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something. -
John Dalton died
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Niels Bohr was born
Bohr found the energy of the colors of light that the hydrogen atom released. He used these energies to find the energies that the single electron in the hydrogen atom could have. Bohr said that the electron had to release energy to change its energy so the differences between the energies of light seen in the atomic spectrum should correspond to the differences in energies of the energy levels. -
The Plum Pudding Model/Raisin Bread Model was created
Thomson’s model was known as the "Plum Pudding Model” (or "Raisin Bread Model.") As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces. -
The Planetary Model was created
Rutherford proposed that atoms consisted of a small dense center filled with positive charges. He named this center the nucleus. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center. He stated these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces. -
The Energy Level Model was created
Bohr’s atom like Rutherford’s contained a dense, positive nucleus. He expanded on Rutherford’s ideas, turning his attention to describing the electron. He stated they moved in fixed, circular orbits (or energy levels) around the nucleus, these called electron shells. These shells were at set distances from the nucleus and were the same for all atoms. He stated they became larger the further away they are from the nucleus, and that electrons furthest from the nucleus have higher energy. -
Lord Ernest Rutherford died
October 19, 1937 -
J.J. Thomson died
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Niels Bohr died
November 18, 1962
