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Atomic Theory, cont’d Chemistry 10/7/14 Drill Write the complete symbol for these atoms. Also, determine if they are ions, isotopes, or both! 40 protons, 51 neutrons, 38 electrons 5 protons, 5 neutrons, 5 electrons 9 protons, 11 neutrons, 10 electrons HW: pg. 4 Atomic Structure Objectives IWBAT Find or calculate atomic mass, atomic number, number of protons, neutrons, and electrons, charge, etc. for any atom Trace the development of Atomic Theory from Democritus to the present day. NOTE: Quiz#3 on Atomic Structure on Friday, 10/10 Rutherford’s Gold-Foil Experiment - 1911 Rutherford and Radioactivity Ernest Rutherford used alpha particles to investigate the gold atom in 1908. We will learn more about alpha particles next week. He conducted a famous experiment that proved that atoms are not solid spheres as proposed by Dalton, or “plumpuddings,” as Thompson said. The Alpha Particles Experiment In his experiment Rutherford used a very thin sheet of gold as a target, and he shot a beam of alpha particles at the gold. alpha particles (-particles) are helium nuclei without electrons, and are a form of radioactivity Nearly all of the alpha particles passed through the thin sheet of gold. Rutherford also noticed that a few particles were deflected from their straight- line path, some by 90 degrees or more. Conclusion The beams were bouncing off the positively charged core of the atoms. Rutherford originally called this a proton, because it was positively charged. Later, it was renamed the nucleus. The nucleus of the atom has almost all the mass of the atom. Therefore, most of an atom is empty space. Bohr Model (the one you all know) Niels Bohr - 1913 Bohr said electrons were in set orbits, like rungs of a ladder. You can only be on one orbit (rung) or the next, not in the middle -- they are quantized Electrons can only move from one to the other by emitting or absorbing a particular wavelength of light (a photon with a certain energy), similar to the metal in the photoelectric effect. Atomic Excitation Picture by Schrödinger's/ Modern model of the atom Particle-Wave Nature of Matter Light has a particle nature (Einstein-1905): photon – quantum of energy that behaves in some ways like a particle Matter has a wave nature (De Broglie-1924): Electrons scatter like X-rays Electron microscopes use this property to see very small things. Heisenberg’s Uncertainty Principle The position and speed of a moving object cannot BOTH be known exactly at the same time. Heisenberg, Cont. Why? The act of observing changes an object. To see things, we must bounce light off of them. To observe an electron, we have to bounce light off of it. The light would move the electron so much that we would not be able to tell where it was, or how fast it was going. Think of hot tea and a cold thermometer. A new idea! Orbitals: A region around the nucleus of the atom where an electron of a given energy is likely to be found. We don’t know exactly where electrons really are, just where they are likely to be. Also called an electron cloud or probability region. So, what’s an orbital?? Orbit Orbital ex. Electron is like a bee around a beehive. Closure What is another metaphor you could use for the Plum Pudding model? How many electrons would Fe3+ have?