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400 BCE
Democritus's Atomic Model
Democritus was an Ancient Greek philosopher who developed the Ancient Atomic Model which said that if one could cut an object enough times he would reach a particle which would not be cuttable. He called this particle 'Atomos' which means indivisible or uncuttable. He suggested atoms had properties of the objects. For example, he believed metal atoms were hard and atoms of pointy objects were sharp. Democritus also proposed that there were two elements, the atoms and the void which they move in. -
Dalton's Atomic Theory
Chemist and meteorologist John Dalton developed an Atomic Model in which he theorized that everything is made of atoms which are impossible to be sub-divided or broken. He also theorized that atoms combine to form compounds during chemical reactions. He also believed atoms could not be created but are rearranged or combined during chemical reactions. He believed these atoms were spheres and wholes like Democritus believed. Dalton's model of an atom is often referred to as a 'solid sphere model'. -
Thompson's Plum Pudding
Thompson in his atomic model theorized that atoms were not invisible particles. He suggested the presence of spread out negatively charged subatomic particles which he called corpuscles and (called electrons today). He was able to find this by using a cathode ray to use high voltage across metal electrodes. The steam from the particles produced from the metal went towards positive charge and away from negative charge which he concluded it meant there were negatively charged subatomic particles. -
Rutherford's nuclear Atomic Model
Rutherford a New Zealand physicist figured out that there was a positively charge center to the atom. He named this the nucleus and meaning nut. He compared this to planets orbiting the sun. The planets being the negatively charged subatomic particles (electrons) and the sun being the positively charged sub atomic particles (protons). He also theorized that the majority of the mass of the atom was in the center. -
Bohr's quantum atomic model
Bohr a Danish Physicist about an year after Rutherford's atomic model. He believed if the electrons kept orbiting, they would lose energy and disrupt the balance of the atom hence he believed Rutherford's atomic model was incorrect. He theorized that shells closer to the nucleus had less energy and shells further away had more energy. His mode is sometimes called the Rutherford-Bohr model as he took major inspiration from Rutherford's atomic model.