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Average Atomic Mass Moles Start Atomic History Chemistry 9/28/15 Drill Pick up the half-sheet for the drill. Put your HW out on the desk to be checked. HW: Average Atomic Mass Calculation Formula Mass and Mole Conversion Practice Problems Objectives IWBAT Calculate the formula mass or molar mass for any compound. Convert between moles, grams, and particles for any element or compound Trace the development of Atomic Theory from Democritus to the present day. HW Review Atomic Structure WS 3-3 Practice Problems WS State the number of moles in 58.4 grams of Carbon. 12.01 g C = 1 mol C 58.4 g C = ? mol C 58.4 g C x 1 mol C = 4.86 mol C 12.01 g C The Mole If you have 10.0 g of water, how many molecules in that amount? 10.0 g H2O x 1 mol x 18.02 g H2O = 6.022 x 1023 molecules 1 mol 3.34 x 1023 molecules of H2O The Mole If you have 25.0 g of copper (II) sulfate, CuSO4, how many formula units are in that mass? 25.0 g CuSO4 x 1 mol 159.61 g CuSO4 = x 6.022 x 1023 formula units 1 mol 9.43 x 1022 formula units of CuSO4 Mole Practice Mass and Mole, Mole and Avogadro’s Number Complete the practice at your desk. Ask Ms. Bloedorn for help if you have questions Average Atomic Mass Go back to the Atomic Structure notes from last week. Let’s finish the bottom! 4A Quiz Review Ms. Bloedorn will hand back your Unit 2 Quizzes— take a look, ask questions, return to her. Let’s take a turn… To HISTORY! Dalton’s Atomic Model - 1805 Atoms are indivisible units of matter that are unique for each element, and combine to make various compounds. A lump of gold is made of tiny gold pieces (atoms). Carbon dioxide is made of tiny carbon and oxygen pieces (atoms) combined together. These atoms cannot be broken down further. Was there any science involved in this model? YES! John Dalton did many scientific experiments, especially with gases, to formulate his ideas. Dalton’s Atomic Theory of Matter Four Postulates: All matter is composed of extremely small particles called atoms. Atoms of the same element are identical, and atoms of different elements are different from those of any other element. Atoms are neither created nor destroyed in any chemical reaction. Atoms combine in definite proportions (the same proportion) to form compounds. Ex. CO vs. CO2 J. J. Thomson – 1898 Thomson took advantage of new technology – the cathode ray tube. Cathode “rays”/particles – negatively charged, very light (but they do have mass— Milliken’s Oil Drop Experiment), came from atoms. Thomson’s Discovery Thomson knew atoms were usually neutrally charged. So, he realized that if he could remove a negative particle, there must be a positively charged part also. Thomson’s Conclusions Thomson’s model of the atom is heterogeneous and solid, but NOT indivisible. Electrons can be removed, so it can be divided. The Plum Pudding Model – Solid sphere of positive charge with electrons spread through it like raisins or plums in a plum pudding. Robert Millikan – 1910 Millikan, using a set-up seen in your diagrams, calculated the charge of the electron using oil drops. This also PROVED that there were such things as subatomic particles—some people still had doubts. It also introduced the idea of a quantized charge. 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 [email protected] 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. Exit Ticket An atom has 12 protons, 11 neutrons, and 10 electrons. Write the full symbol and full name for this atom. Calculate the average atomic mass of this element, using the data. Show your work: Mass number (amu) Natural abundance (%) 10 19.9 11 80.1 How many moles are in 6.022 x 1025 molecules?