CHM 101 1st Edition Lecture 2 Outline of Last Lecture - Matter- Measurements- ConversionsOutline of Current LectureI. Scientists that contributed to ChemistryII. Atomic theoryIII. Atomic StructureIV. IsotopesV. Periodic TableCurrent Lecture400 B.C- Democritus proposes atomic theoryo All matter is made up of atoms which are hard, indivisible, and in constant motion- Plato and Aristotle believed nothing is indivisibleAtomic theory- John Dalton proposes his atomic theory (1803-1807)o Elements are made up of atomso All atoms of a given element are identical in mass and other properties o Atoms cannot be created or destroyedo Atoms from different elements can combine to form compounds - The Law of Constant Compositiono In one compound the number of atoms and type is constant- The Law of Conservation of Mattero When a chemical reaction occurs matter is not created or destroyed Discovery of Atomic Structure- JJ Thompson discovered the electron with a cathode ray tube o Discovered a beam of electrons that were attracted to the positive plate end of the tubeo Calculated a charge to mass ratio of the electron Charge of e- = 1.76 x 108 Mass of e-- Robert Millikano Oil drop experimento Determined the charge of a single electrono Measured the negative charges of oil dropso The oil drops were always in multiples of 1.60 x 10-19o Mass of electron 9.10 x 10-28 Discovered by using Millikan’s formula- Thompson knew matter was neutral and there must also be a positive chargeo Plum-pudding model- Edward Rutherfordo Gold foil experimento α-scattering experimentso Shot positive particles at gold foil Most particles went through the foil Some were deflected- Were deflected by the positive charge in the middleo Discovers positive nucleuso Most of the atom is empty spaceModern view of the atomic structure - “electron cloud”o Contains electronso Outside the nucleus of the atomo All of the negative charge in an atomo Very little masso Most of the volume of the atom- Nucleuso Contains protons and neutronso All of the positive charge o Nearly all of the mass of the atomo Very little volume-dense- Each element has a charatcteristic number of protons- Atomic number- number of protons in the nucleus of an atom of a particular element- Neutral atoms have the same number of protons and electrons- Mass number- total number of protons and neutrons in the nucleus of an atom- Isotope- differing number of neutrons in the same elementIsotope # of Protons # of Neutrons # of Electrons 28 Si1414 14 1429 Si1414 15 1430 Si 14 16 141420 Ne1010 10 1032 S1616 16 163 Atomic numberLi Atomic Symbol6.939 Atomic weight- Almost all elements exist naturally as a mixture of isotopes - Atomic weight- average atomic mass- Natural distribution of an element’s isotopes is used to calculate its atomic weight- Atomic weight = ∑ ((isotope mass) x (fraction of isotope abundance))o Example: Sample of C is 98.89% 12C (12.000 amu) and 1.110% 13C (13.003 amu).What is the atomic weight?(.9889)(12.00 amu) + (0.01110)(13.003 amu)11.867 amu + 0.144 amu =12.01 amuPeriodic Table- Periods-rows of the periodic table- Groups- columns of the periodic table- Metals- shiny, good conductors of heat and electricity, except mercury (left side of periodic table)- Non-metals – poor conductors (left on the periodic table)- Metalloids- properties between metals and nonmetals (starts with Boron on the periodic table)- Group 1A – Alkali Metals- Group 2A – Alkaline Earth Metals- Group 6A – Chalcogens- Group 7A – Halogens- Group 8A – Noble gasesSide note- it would be really helpful for the class to try to memorize the first three rows of the periodic table because they are the most commonly used
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