Atomic History and Models for KS3 Science
- 1. History and Models of the Atom Year 8 Science
- 2. • Believed universe made of invisible units called atoms • Named them Atoms • 400 BC • Aristotle said “He’s a quack!!!” • Took 2000 yrs to be proved right! Democritus
- 3. The “Billiard Ball” Model proposed by John Dalton in 1804 this theory proposed that matter was composed of small, spherical particles but evidence was later gathered that matter was composed of even smaller bits
- 4. Thomson: “Plum Pudding” or “Chocolate Chip Cookie” Model using available data on the atom, J.J. Thomson came up with the idea of having charges embedded with Dalton’s Billiard Balls Also used cathode ray experiment to discover the existance of the electron positive (evenly distributed) “dough” part negative “chocolate” note: this model kept Dalton’s key ideas intact
- 5. Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron Click on me: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
- 6. Nuclear Model Ernest Rutherford discovered a huge flaw in the previous concept of the atom during his now famous gold foil experiment
- 7. Rutherford Discovered the Nucleus and the Positive Protons Surmised atoms are made of mostly empty space Didn’t know about the Neutrons Famous Gold Foil Experiment Click on me: http://www.mhhe.com/physsci/chem istry/essentialchemistry/flash/ruther 14.swf
- 8. Gold Foil Experiment • Particles shot through thin sheet of gold • Most shots went straight through • A small amount were deflected • Hence… The atoms must be made of mostly empty space with a small dense nucleus
- 9. If previous models were correct alpha particles would have passed straight through the the gold Further explanation of Nuclear Model
- 10. Rutherford found that most (99%) of the alpha particles that he shot at the gold went straight through From these experiments Rutherford concluded that the atom had a dense positive core, with the rest composed of mostly empty space with the occasional negatively charged electron Nuclear Model + - - - - - note: this model completely changed the definition of atom
- 11. Rutherford’s Findings #1 The nucleus is small #2 The nucleus is dense #3 The nucleus is positively charged * Most of the particles passed right through * A few particles were deflected * VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:
- 12. Niels Bohr Discovered that electrons exist in several distinct layers or levels “Jimmy Neutron Model” Travel around nucleus like planets travel around sun Electrons Orbit Electrons can jump between levels with energy being added/released
- 13. Bohr Model Niels Bohr proposed that electrons revolve around the central positive nucleus (like planets in the solar system) negative electrons 3 positive protons
- 14. Bohr Model Bohr also suggested that the electrons can only revolve in certain orbits, or at certain energy levels (ie, the energy levels are quantized) no energy level in between steps