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are Chemistry101 Chapter2 Atoms,MoleculesandIons FundamentalChemicalLaws There three important fundamental laws that govern all chemistry Lawofconserva<onofmass Massisneithercreatednordestroyed AntoineLavoisier Mass cannot be created/destroyed, although it may be rearranged in space, and changed into different types of particles. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products. CH4 + 2O2 CO2 + 2H2O XgXg Example In a combustion reaction, 46.0 g of ethanol reacts with 96.0 g of oxygen to product water and carbon dioxide. If 54.0 g of water is produced, what mass of carbon dioxide is produced? FundamentalChemicalLaws There are three important fundamental laws that govern all chemistry Lawofdenitepropor<on Agivencompoundalwayscontainsexactlythesame propor:onofelementsbymass. JosephProust A chemical compound always contains exactly the same proportion of elements by mass. An equivalent statement is the law of constant composition, which states that all samples of a given chemical compound have the same elemental composition. Any amount of water (H2O) is composed of 8/9 O atoms and 1/9 H atoms regardless of the mss of the sample Example A sample of chloroform (CHCl3) is found to contain 12.0 g of carbon, 106.4 g of chlorine and 1.01 g of hydrogen. If a second sample of chloroform is found to have 30.0 g of carbon, what is the total mass of chloroform in the second sample? Example Three samples of a solid substance composed of elements A and Z were prepared. The first contained 4.31 g of A and 7.70 g of Z. The second sample was 35.9% A and 64.1% Z. It was observed that 0.718 g of A reacted with Z to form 2.00 g of the third sample. Show that these date illustrate the law of definite composition. FundamentalChemicalLaws There are three important fundamental laws that govern all chemistry Lawofmul<plepropor<ons(Dalton): Whentwoelementsformaseriesofcompounds,the ra:osofthemassesofthesecondelementthatcombine with1gramoftherstelementcanalwaysbereduced tosmallwholenumbers. JohnDalton When chemical elements combine, they do so in a ratio of small whole numbers. CO, CO2 exist. CO1.3 does not Example Indium oxide contains 4.784 g of indium for every 1.000 g of oxygen. Before 1869 chemists believed that the formula for indium oxide was InO. In 1869, Mendeleev presented his version of the periodic table and proposed a molecular formula of In2O3 for indium oxide. Assuming that oxygen has an atomic mass of 16.00 show that Mendeleevs assignment agrees with our modern view of the periodic table. DaltonsAtomicTheory The fundamental chemical laws provided for the basis of Daltons Atomic Theory which formed our understanding of the atom. I - Each element is made up of tiny particles called atoms II All atoms of a given element are identical III The atoms of a given element are different from those of any other element The atoms of different elements can be distinguished from one another by their respective relative atomic weights. DaltonsAtomicTheory The fundamental chemical laws provided for the basis of Daltons Atomic Theory which formed our understanding of the atom. IV Chemical compounds are formed when atom of different elements combine with each other A given compound always has the same relative numbers and types of atoms DaltonsAtomicTheory The fundamental chemical provided laws for the basis of Daltons Atomic Theory which formed our understanding of the atom. V Atoms cannot be created, divided into smaller particles, nor destroyed in a chemical process A chemical reaction simply changes the way atoms are grouped together GayLussacsResults GayLussac Measured(undersamecondi:onsofTandP)the volumesofgasesthatreactedwitheachother. AvogadrosHypothesis AtthesameTandP,equalvolumesofdierentgases containthesamenumberofpar:cles. Avogadro hypothesized that two given samples of an ideal gas at the same temperature (T), pressure (P) and volume (V) contain the same number of molecule. Thus, the number of molecules or atoms in a specific volume of gas is independent of their size or the molar mass of the gas. This is now considered a truth and is referred to as Avogadros Law. This hypothesis helps us understand Gay-Lussacs observations InterpreCngGayLussacsResults 2H2 + O2 2H2O InterpreCngGayLussacsResults H2 + Cl2 2HCl Example 1 L of chlorine (Cl2) reacts with 3 L of fluorine (F2) to give 2 L of a gaseous product. All volumes are at the same temperatures and volumes. What is the formula of gaseous product? AtomicStructureEarlyExperiments Scientists became interested in the structure of the atom that is, what is the atom composed of and how is it held together. J.J.Thomson(18981903) Postulatedtheexistenceofelectronsusing cathoderaytubes. Determinedthechargetomassra:oofan electron. Theatommustalsocontainposi:vepar:clesthat balanceexactlythenega:vechargecarriedby par:clesthatwenowcallelectrons. ThomsonsExperiment Applying high voltages to a cathode-ray tube resulted in a ray produced at the positive electrode that travelled to negative electrode. http://www.youtube.com/watch#!v=O9Goyscbazk&feature=related ThomsonsExperiment Conclusion 1: The ray was a stream of negatively charged particles (electrons) Conclusion 2: All atoms must contain electrons Conclusion 3: The charge-to-mass ratio of an electron is -1.76 x 108 C/g Thomson proposed a structure of an atom as a spherical cloud of positive charge with the negatively charged electrons are suspended The Plum Pudding Model AtomicStructureEarlyExperiments RobertMillikan(1909) Performedexperimentsinvolvingchargedoildrops. Determinedthemagnitudeofthechargeona singleelectron. Calculatedthemassoftheelectron. MillikansExperiment http://www.youtube.com/watch?v=XMfYHag7Liw MillikansExperiment Conclusion 1: The charge on an electron is 1.602176487(40)1019 C Conclusion 2: The mass of the electron is 9.111019 kg AtomicStructureEarlyExperiments ErnestRutherford(1911) Explainedthenuclearatom. Atomhasadensecenterofposi:vechargecalled thenucleus. Electronstravelaroundthenucleusatarela:vely largedistance. RutherfordsGoldFoilExperiment http://www.youtube.com/watch?v=5pZj0u_XMbc RutherfordsGoldFoilExperiment Conclusion 1: The atom is not a spherical cloud of positive charge and electrons Conclusion 2: Atom has a dense center of positive charge called the nucleus ModernViewofAtomicStructure The work of Thomson, Millikan & Rutherford laid the ground work for our current view of the structure of the atom Theatomcontains: Electronsfoundoutsidethenucleus;nega:vely charged. Protonsfoundinthenucleus;posi:vecharge equalinmagnitudetotheelectronsnega:ve charge. Neutronsfoundinthenucleus;nocharge; virtuallysamemassasaproton. ModernViewofAtomicStructure ... View Full Document

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