CHM1045 Lecture 4 Outline of Last Lecture I Dimensional Analysis Method of Solving Problems Outline of Current Lecture I Daltons Atomic Theory II Cathode Ray Tube III Millikan s Experiment IV Rutherford s Experiment V Chadwick s Experiment VI Atomic Mass Isotopes VII Molecules VIII Ions Current Lecture Daltons Atomic Theory 1 Elements are composed of extremely small particles Called atoms 2 All atoms of a given element are identical having the same size mass and chemical properties The atoms of one element are different from the atoms of all other elements 3 Compounds are composed of atoms of more than one element In any compound the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction 4 A chemical reaction involves only the separation combination or rearrangement of atoms it does not result in their creation or destruction Ex Carbon Monoxide O C 1 1 Carbon Dioxide O C 2 1 Law of Multiple Proportions Ex 16 X 8 Y 8 X2Y Law of Conservation of Mass Cathode Ray Tube shooting an electron to show it s negative change Millikan s Experiment They could measure the mass of the electron E 1 60 10 19C Rutherford s Experiment Shot a positive particles and a gold foil Shows that the nucleus isn t organized Proton has opposite charge then electron Small volume in atom Chadwick s Experiment Found that HE had neutrons also H 1 H 2 Found that the neutron has no charge Contains neutrons equal in mass to protons Atomic Mass Isotopes 1 Atomic Number Z of protons in the nucleus 2 Mass Number A of protons plus neutrons Atomic of neutrons 3 Isotopes atoms of the same element X with different number of neutrons in nuclei XAZ Example 1 How many protons electrons and neutrons are in the following a NA2011 11 protons 11 electrons 20 11 9 neutrons b NA2211 11 protons 11 electrons 22 11 11 neutrons c O17 8 protons 8 electrons 17 8 9 neutrons d Carbon 14 C146 6 electrons 6 protons 8 neutrons Review Which of the following two symbols provides more information 17O or O 8 17O because its provides more information then 8O Molecule Molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces Ex H2O NH3 Diatomic molecule contains only two atoms Ex H2 N2 O2 Polyatomic molecule contains more than two atoms Ex O3 H2O NH3 CH4 Ions Ion is an atom or group of atoms that has a net positive or negative charge Cation ion with a positive chargeIf a neutral atom loses one or more electrons it becomes a cation Na 11 protons and 11 electrons Na 11 protons and 10 electrons anion ion with a negative chargeIf a neutral atom gains one or more electrons it becomes an anion Cl 17 protons and 17 electrons Cl 18 electrons and 17 protons monatomic ion contains only one atom Na Cl Ca2 O2 Al3 N3 polyatomic ion contains more than one atom OH CN NH4 NO3
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