ATOMIC STRUCTURE By: Emily Landers & Alex Strickland Aristotelian Atomic Theory Ancient Greeks believed that there were only four elements that everything was made up of: EARTH WATER AIR FIRE More of Aristotle… All earthly substances originate from these four elements. When comparing a tree to a rock, different amounts of the four elementals exist in each to create the differences we see or observe. The elements were “pure” but could not be found in the state on earth. Every visible thing was made up of combinations of earth, water, air, and fire. && some more ARISTOTLE.. While we do know now that theses previous theories are false, in a way the four elements do align with the four states of matter that modern science has agreed on: solid (earth), liquid (water), gas (air), and plasma (fire). Cathode Ray Experiment Cathode-ray tubes supplied evidence of the existence of electrons, which are negatively charged subatomic particles that have relatively little mass. This then lead to the Plum Pudding Model… Plum Pudding Model In J.J. Thomson’s Plum Pudding Model each atom was a sphere filled with a positively charged fluid. The fluid was called “pudding”. Scattered in this fluid were electrons known as the “plums”. Plum Pudding continued The plums pudding model was proposed in 1904 before the discovery of the atomic nucleus. It has also been called the 'chocolate chip cookie model or "Blueberry Muffin Model" Dalton’s Solid Sphere Model Also known as the Billiard Ball Model He described atoms as indivisible spheres with constant density throughout. Dalton also said that all atoms of the same element were identical and different from those atoms composing another element. This was not accurate. J.J. Thomson conducted a new experiment That didn’t prove it wrong, but added on information to it. Rutherford’s Nucleus Model Rutherford took a piece of gold foil. The gold foil was secured so that particles from a radioactive source (Polonium) could be directed at the gold foil. A fluorescent screen was used to detect where the radioactive particles ended up. Most of the alpha particle went right through the gold foil unaffected. A few were deflected and even fewer were reflected off the gold foil. These astounding discoveries led to Rutherford's Model of the atom: Atoms are not solid masses. Most of the atom is made up of space as indicated by the fact that most of the radioactive particles went right through the foil unaffected. The atom has a central, small, solid, and positively charged part that Rutherford called the nucleus. Gold Foil Experiment If J.J. Thomson’s theory was correct then the alpha particles should have gone straight through the atom, but as shown in the model below…that did not happen. The Atomic Model Bohr solar system model This model was proposed by Niels Bohr in 1915 . In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. Electron Cloud Electron Cloud Model (1920's)- an atom consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels. Erwin Schrodinger and Werner Heisenburg developed probability functions to determine the regions or clouds in which electrons would most likely be found.