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Atomic Structure Timeline
Transcript of Atomic Structure Timeline
Democritus's Uncuttable Atom A Greek Philospher named Demicritus described the atom as a solid particle that could not be divided into smaller pieces 1904 Danish physicist Niels Bohr improved upon the Rutherford model and hypothesized that electrons followed a specific path. He also said that the nucleus was made up of protons (particles with a positive charge) and neutrons (particles with no charge. 1913 Bohr Model present Electron Cloud Model Thomson Model English physicist Joseph John Thomson inferred from his studies that negatively charged electrons were embedded into the positively charged atom like chocolate chips in a cookie. He also explained that protons were smeared on the atom to keep it neutral. Rutherford Model 1911 Ernest Rutherford (a British physicist) proposed that almost all the mass of the atom was concentrated in a nucleus surrounded by electrons. Today's model explains that the nucleus of an atom is surrounded by a field of energy (called the electron cloud) where electrons randomly appear at different times. There are a specific number of electrons in each energy level. The nucleus of an atom is still accepted as being made up of neutrons and protons. Quarks (smaller particles that make up protons and neutrons) were also discovered. around 400 B.C From old to new The old atomic models did not provide enough information about the atom. Democritus's model was too basic because of the lack of technology back in ancient times. After Thomson discovered the electron (using a cathode ray tube), Rutherford and two other scientists developed an experiment that disproved the placement of the electrons. Gold Foil Experiment In this experiment Hans Geiger, and Ernest Marsden fired a beam of alpha particles (one of the types of radiation given off by radioactive elements) at a thin metal sheet. Most of the alpha particles traveled through the foil but a small fraction of it bounced back and ended up on the same side of the foil as the incoming beam . This meant that some of the alpha particles ran into huge concentrations of positive charge. From this Rutherford theorized that all the positive charge is crammed in the center (the nucleus) and that the lighter electrons, he assumed, circle around the nucleus in orbits. From old to new cont. The Rutherford model was still incomplete. Bohr proved the existence of neutrons and stated that electrons followed specific paths. However, this was disproved in today's model. Importance of atoms Atoms make up everything in our universe. They are the basic building blocks of life. Without atoms there would be no matter at all. Nothing would exist.