CHEM 241 Chapter 2 Atoms molecules and ions.pdf - Chapter 2...

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Chapter 2Atoms, Molecules andions
2.1The Early History of ChemistryGreeks were the first to attempt to explain whychemical changes occur.Alchemy dominated for 2000 years.Several elements discovered.Mineral acids prepared.Robert Boyle was the first “chemist”.Performed quantitative experiments.Provided evidence for the atoms and definedthe nature of an element.
2.2Fundamental Chemical LawsLaw of conservation of mass (Lavoisier):Mass is neither created nor destroyed.Three Important LawsTotal mass of reactants = Total mass of productsmercury + oxygenmercury (II) oxide2.53 g( ? )2.73 g
Law of definite proportion (Proust):A given compound always contains exactly thesame proportion of elements by mass.Three Important Laws (continued)1.000 gNaCl :0.3934 gNa+0.6066 gCl100 gH2O:11 gH+89 gO
Law of multiple proportions (Dalton):When two elements form more than onecompound, the masses of one element in thesescompounds for a given mass of other elementare in ratio of small whole numbers.C and O inCO (1.000 g C and 1.332 g O)CO2(1.000 g C and 2.664 g O)The mass of O in CO2is exactly twice of that in COThree Important Laws (continued)
2.3Dalton’s Atomic TheoryAll mater is composed ofatoms(H, O, Cl,….)Dalton’s Atomic Theory (1808)An element: is a type of matter composed of onlyone kind of atom(He, H2, O2, Ag,….)A compound: is a type of matter composed of atomsof two or more elements chemically combined infixed proportions(H2O, CO2, SiO2, CaCO2,….)
A chemical reactions:consists of the rearrangementof atoms present in the reacting substances to givenew chemical combinations in the productsC3H8+5O23CO2+4H2O(atoms are not created or destroyed by chemical reaction)Dalton’s Atomic Theory (continued)
GayLussacMeasured (under same conditions of T and P) thevolumes of gases that reacted with each other.

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