History of the atom
- 2. The History of the Atom
- 3. The Early Greek Theories Continuous Theory-all samples of matter can be continuously subdivided into smaller and smaller pieces indefinitely. Proposed by Aristotle Discontinuous Theory-samples of matter can not be continuously subdivided--there is a smallest piece(atom). Proposed by Democritus No one ever believes me Of course everyone believed me.
- 4. Laws which caused doubt in Aristotle ’s Theory
- 5. #1 Law of Conservation -matter can neither be created nor destroyed in ordinary chemical reactions.(Developed by Antoine Lavoisier) I developed this law a few years before I lost my head on the guillotine
- 6. #2 Law of Definite Composition -compounds contain the same percentage by mass of each element no matter what the source of the compound. (Developed by Joseph Proust) It ’s all the same to me.
- 7. #3 Law of Multiple Proportions -elements can combine in more than one ratio to form more than one compound. (Developed by John Dalton) Flexibility is a good thing. Examples H 2 O and H 2 O 2 Water and Hydrogen Peroxide CO and CO 2 Carbon monoxide and Carbon dioxide
- 8. These questions lead John Dalton to reject Aristotle ’s theory and create a theory of his own.
- 9. Dalton ’s Atomic Theory Matter is composed of small indivisible pieces called atoms. Atoms are indestructable. All atoms of the same element are identical. All atoms of different elements are different. Atoms combine in whole number ratios to form compounds.
- 10. The result of this Theory was the creation of Dalton ’s Model of the atom. Solid indestructable sphere.
- 11. Discovery of the Sub-atomic Particles
- 12. THE ELECTRON The electron was discovered by J.J. Thomson in 1899. Thomson ’s work involved the use of a cathode ray tube. The development of the cathode ray tube lead to the invention of the television. Little did I know TV would turn our brains to mush.
- 13. Thomson ’s Model of the Atom Represents negative electrons dispersed in positive surroundings.
- 14. THE PROTON The proton was discovered by Ernest Rutherford in 1909 during his famous gold foil experiment. Rutherford ’s model of the atom was rejected because it failed to obey the laws of physics as they were known at that time. What do those physicist know anyhow.
- 15. Rutherford ’s Model of the Atom Electron traveling on a curved path around the nucleus. Small dense positively charged nucleus. The gold foil experiment determined that atoms are mainly empty space.
- 16. THE NEUTRON Discovered in 1932 by James Chadwick, the neutron was the last sub-atomic particle to be found. The lack of a charge made the neutron difficult to detect. Neutrons are called the glue of the nucleus and their importance was not fully understood until nuclear chemistry became a reality. Yes, I know I look like a nerd.
- 17. The Bohr Model According to classical physics, a charged particle traveling on a curved path, like the electron in the Rutherford model, will lose energy. This would eventually cause the electron to drop into the nucleus destroying the atom. Bohr proposed that electrons don ’t obey the laws of classical physics but have their own set of laws now known as quantum physics.
- 18. In the Bohr model of the atom, electrons can travel only on certain paths which are stable and do not lose energy. Bohr even calculated how many electrons could travel each path in his model. The formula used to calculate the number of electrons on each level was #e - = 2n 2 Where n represents the energy level number. Example: Energy level #3 #e - =2(3) 2 = 18
- 19. Heisenberg Uncertainty Principle Werner Heisenberg stated that it was not possible to know both the speed and location of an object at the same time. By measuring one, you changed the other. This disproved Bohr ’s model of the atom because Bohr described absolute positions for his electrons which according to Heisenberg were not possible. The search began for a better explanation and model.
- 20. The Current Model of the Atom The invention of the supercomputer allowed mathematician Irwin Schrodinger to pull all this information together and create the current model of the atom called the Quantum Mechanical Model of the atom. The current model of the atom is based on the probability of finding an electron in a three dimensional region of space known as an orbital. Work continues on Atomic theory with the discovery by Gell-mann and Zweig of the quark, which makes up protons and neutrons and many even small particles.
- 21. The Current Model of the Atom These all fit together to form the current model of the atom. “ s” orbital “ p” orbital
- 22. The Quantum Mechanical Model
- 23. The End