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NOTES 2.2 The law of multiple proportions: when two elements form a sense of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. 2.3 Dalton’s theory http://www.kentchemistry.com/links/AtomicStructure/dalton.htm Dalton's Model of the Atom Before we can discuss Dalton's Model of the atom, I must first mention the Law of Multiple Proportions. Simply put, when elements combine to form compounds they do so in whole number ratios. Carbon and Oxygen can form either CO ( a 1:1 ratio) or CO2 (a 1:2 ratio). It also states that if the mass of the first element is constant the second elements masses would be in a whole number ratio. 1.00g of Carbon will have combined with 1.33g in CO 1.00g of Carbon will have combined with 2.66g in CO2 The mass are in a 1:2 ratio Simply put if combinations are in whole number ratios, there must be a one. This one being an atom. Here are Dalton's assumptions. All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements. 2.4 J.J Thomson http://www.kentchemistry.com/links/AtomicStructure/JJThompson.htm When investigating cathode rays using a highly evacuated discharge tube he was able to use the calculated velocity and deflection of the beam to calculate the ratio of electric charge to mass of the cathode ray. This was found to be constant regardless of the gas used in the tube and the metal of the cathode and was approximately 1000 times less than the value calculated for hydrogen ions in the electrolysis of liquids. The electron is discovered, J J Thomson publishes his discovery of a subatomic particle common to all matter. The New Model of the Atom-Thompson knew atoms were neutral, so there must be a balance of negative and positive particles. This new model is referred to as the Plum Pudding Model. THERE IS A GREAT VIDEO ABOUT IT THAT CAN HELP YOU UNDERSTANDING Millikan http://www.kentchemistry.com/links/AtomicStructure/Millikan.htm The oil drop experiment was an experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). The experiment entailed balancing the downward gravitational force with the upward buoyant and electric forces on tiny charged droplets of oil suspended between two metal electrodes. Since the density of the oil was known, the droplets' masses, and therefore their gravitational and buoyant forces, could be determined from their observed radii. Using a known electric field, Millikan and Fletcher could determine the charge on oil droplets in mechanical equilibrium. By repeating the experiment for many droplets, they confirmed that the charges were all multiples of some fundamental value, and calculated it to be 1.5924×10−19 C, within one percent of the currently accepted value of 1.602176487×10−19 C. They proposed that this was the charge of a single electron. With this data and J.J. Thompsons charge to mass ratio the mass of the electron could be calculated. 1.5924×10−19 C 1 gram x -28 1.76 x 108 C = 9.04 x 10 g or 9.04 x 10 -31 the accepted kg value is 9.109 x 10-31 kg CHENK OUT THE VIDEO ON LINE TO GET CLEAR! Rutherford http://www.kentchemistry.com/links/AtomicStructure/RutherfordTutorial.htm Rutherford's Gold Foil Experiment Tutorial The experiment to probe the structure of the atom performed by Hans Geiger (Geiger counter) and Ernest Marsden in 1909, under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester. The Experiment A beam of alpha particles, generated by the radioactive decay of radium, was directed onto a sheet of very thin gold foil. The gold foil was surrounded by a circular sheet of zinc sulfide (ZnS) which was used as a detector: The ZnS sheet would light up when hit with alpha particles. THESE THEORIES NEED TO BE MEMORIZED COULD BE ON MULTIPLE CHOICE 2.5 the nucleus is assumed to contain protons, which have a positive charge equal in magnitude to the electron’s negative charge, and neutrons which have virtually the same mass as a proton but no charge. PICTURE 2.8 Formulas from names Acids PropertiesProduce H+ (H3O+) in water as the only positive ion. Acids are electrolytes. They ionize and conduct electricity in water. ex. HCl(aq) Dilute quantities taste sour. ex. Citric Acid Corrodes metals to produce hydrogen gas (H2) Concentrated Acids are CAUSTIC, they cause chemical burns to skin. Turn Blue Litmus Red Phenolphthalein turn colorless Neutralizes Bases pH less than 7 CHECK THIS OUT http://link.brightcove.com/services/player/bcpid1155269983?bctid=1405310652 http://link.brightcove.com/services/player/bcpid1155269983?bctid=1396941707 http://link.brightcove.com/services/player/bcpid1155269983?bctid=1396937749 Proton (p+) is positively charged particle of the atomic nucleus. The atomic number of an element represents the number of protons in the nucleus. Electron (e-) is negatively charged particle that can occupy a volume of space (orbital) around an atomic nucleus. All atoms of an element have the same number of electrons (i.e. any Chlorine atom is going to have 17 electrons). Electrons can be shared or transferred among atoms. Atoms have an equal number of protons and electrons; therefore, they have a no net charge. Ion is an atom that has gained or lost one or more electrons, thus becoming positively or negatively charged. Neutron is an uncharged particle of the nucleus of all atoms EXCEPT hydrogen. For a given element, the mass number is the number of protons and neutrons (nucleons) in the nucleus. Isotope is one of two or more forms of atoms of an element that differ in their number of neutrons. They have the same atomic number (same number of protons and electrons), but a different mass number due to more or fewer neutrons. Particle Relative Charge Charge** Mass Relative mass** Location 1.672 Proton +1.60 x 10 -19 C +1 x 1024 Electron -1.60 x 10 C -1 - x 10 28 nucleus g 9.05 -19 1 amu g 0 amu ~(1/1840 amu) electron cloud (orbital) 1.674 Neutron neutral 0 x 1024 1 amu nucleus g **Using relative charges and masses are used to keep calculations simple. Atomic Number The atomic number is the number of protons in the nucleus of an atom. It is listed on the periodic table for each element. No two elements have the same atomic number (or the same number of protons), so the atomic number identifies the element.(symbol: Z) Mass Number Mass number: (symbol: A) total number of protons and neutrons in the nucleus (not listed on the periodic table, since it varies). NOTE this number is a whole number. Atomic Mass is different. Atoms of the same element have the same atomic number, but may have different mass numbers. Isotopic notation for a particular atom (also called nuclide symbol notation): A E Z (E = element's symbol; A = mass number; Z = atomic number) For example: 23 11 Na Represents a sodium atom which always has 11 protons and in this case has a mass number of 23. (Note: This means that there are 12 neutrons. 23 - 11 = 12) Mass number - atomic number = # neutrons Determining the number of electronsThe number of electrons in an element can change. For a neutral atom, the number of protons is exactly equal to the number of electrons. So the number of electrons is the same as the atomic number. However, it is possible to remove electrons and not change the identity of an element. These are called ions. The charge on the ion tells you the number of electrons. If the charge is positive, subtract that number from the atomic number to get the number of electrons. You have more protons. If the charge is negative, add the amount of charge to the atomic number to get the number of electrons. You have more electrons. Determine the number of protons, neutrons, and electrons present in each of the following atoms. (mass # = top number, atomic # = bottom number) a) 28 a 14Si electrons protons = 14, = 14, neutrons = 14 b) 197 b 79Au c) n = 118 40 c 18Ar d) d p = 29, e = 29, n 29Cu = 35 39 e p = 19, e = 19, n 19K f) p = 18, e = 18, n = 22 64 e) p = 79, e = 79, = 20 133 f p = 55, e = 55, n = 78 55Cs Identify atoms that are isotopes in each of the following sets of four atoms. A) 80 X 35 82 35 81 X 36 X A 80 35 X 82 35 X B) 19 19 X 9 C) 10 17 X 23 X D) 70 33 X X 8X 11 70 34 X 19 B 17 X 9 24 11 20 X 9 9 25 X 11 X 70 70 31 X32X C all D none W tThe symbol, atomic number and atomic mass for the atoms with the following characteristics. 1. 1. Contains 15 neutrons and 13 protons. 2. 3. 4. 33? 9. Copper that lost 2 electrons and has 30 neutrons. 10. Hydrogen that has 2 neutrons and no electrons. 75 As 58 Fe 26 5. 5. Rubidium that contains 87 nucleons. 8. An atom with number of neutrons 15 and mass number Nb 33 d) 4. Iron contains 84 subatomic particles. 18 electrons? 93 41 c) 3. Contains 33 electrons and 42 neutrons. 7. An ion with atomic number 16, mass number of 32 and Al 13 b) 2. Atomic number is 41. Neutrons 52. 6. An ion with 17 protons, 18 neutrons and 18 electrons? 28 87 Rb 37 6. 35 17 7. 32 16 8. 33 18 9. 59 29 10. 3 1 Cl S 1- 2- Ar Cu H 2+ +