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Electron Orbitals "I think it is safe to say that no one understands quantum mechanics." Physicist Richard P. Feynman Electron Orbitals The nature of the nucleus was determined using radiation (Rutherford’s gold foil experiment) The quantum nature of electrons was demonstrated by Bohr using spectroscopy. Using quantum numbers, electrons are defined as occupying orbitals within successively larger shells. Each orbital can contain 2 electrons of opposite spin Electron Orbitals What do electron orbitals look like? Although math could be used to describe the energy of electrons, what they are doing, or what they really are was still very unclear. Are electrons particles? Waves? Both? Something else? Louis de Broglie (1892-1987) Electron Orbitals Louis de Broglie (1892-1987) was a french physicist. In 1922, he hypothesized that not only electrons, but ALL matter exhibits both particle AND wave-like properties. However, the larger the particle, the smaller the wave-like properties become. Electron Orbitals The de Broglie hypothesis stated that: Any moving particle or object has an associated wave. This united Einstein’s work on light and matter, and created a new branch of physics, called wave mechanics. Electron can be thought of as standing waves. (think skipping ropes) Electron Orbitals Erwin Schrödinger (1887 – 1961) Electron Orbitals In 1926, Erwin Schrödinger discovered a set of equations that described the structure of orbitals. His math was based on Louis de Broglie’s concept of electrons as waves. This was the one of the earliest formulations of Quantum mechanics. Electron Orbitals Schrödinger’s equations defined the most probable position of an electron in an atom. An orbital is defined as the area within which the electron will most likely be found. Orbitals are not uniform; within all orbitals, there are different probabilities of where the electron will be. Electron Orbitals probability Hydrogen nucleus The hydrogen atom has one electron in a 1s orbital. As the distance from the nucleus 0.05 0.15 increases, the probability of the Distance from electron occurring at that point nucleus in nm first increases, then diminishes to the point of virtual nothingness Electron Orbitals probability However, we must think in 3D. The probability of finding the 0.05 0.15 electron is the Distance from same no nucleus in nm matter which direction we choose Electron Orbitals Electron orbitals can be thought of as an electron cloud. This cloud is a probability map of where electrons are most likely to be found around the nucleus. The opacity of the cloud is proportional to the probability density. Electron Orbitals Orbitals can thus be viewed as a 3D electron probability density map that outlines the area the electron is probably found. The shape of an orbital is determined by the 2o quantum number, l. The orientation is determined by the magnetic number, ml. 1s (l = 0, ml = 0) z y x 2s (l = 0, ml = 0) z y x 2p (l = 1, ml = 0) z y x 2p (l = 1, ml = -1) z y x 2p (l = 1, ml = +1) z y x Werner Heisenberg Quantum Mechanics Simultaneously, Werner Heisenberg also developed a set of equations that explained the behaviour of electrons. This was called matrix mechanics. However, the math was so complicated, that Heisenberg himself did not fully understand why it explained the quantum nature of electrons. Quantum Mechanics Heisenberg and Schrödinger’s discoveries gave birth to quantum mechanics. Quantum mechanics explains (and makes predictions!) about the natural laws that govern at the molecular level. Quantum Mechanics One of the consequences of quantum mechanics is that it is not possible to simultaneously know the position and momentum (speed and direction) of a particle. This was determined by Heisenberg, and is hence called the Heisenberg Uncertainty Principle. Quantum Mechanics Essentially, the Uncertainty Principle exists because to determine the property of a particle, one must interact with it. This interaction with the particle will alter the properties of the particle. At the atomic level, the interactions between particles becomes very significant. Thus, the smaller the system to be observed, the greater the effect of the Uncertainty Principle Review Questions Page 219 #1-11 (true/false) #12-19 (multiple choice) Pg 220 #4-6, 9-17 (short answer)

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posted: | 8/14/2012 |

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