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Chapter 2: Atoms, Molecules, and IonsSection 2.1— The Early History of ChemistryEarly History of ChemistryGreeks were the first to attempt to explain why chemical changes occurAlchemy dominated for 2000 yearsSeveral elements discoveredMineral acids preparedRobert Boyle was the first “chemist”Performed quantitative experimentsDeveloped first experimental definition of an elementSection 2.2 – Fundamental Chemical LawsConversions Using PrefixesConvert 347 ng to kgConvert 0.00123 in to mSquare Unit ConversionA soccer field has a grassy area that is 1.452 x 104m2. If a lawn mower can cut 468in2/minute, how many hours will it take to mow the field (1 in=2.54 cm)?One More ConversionA CD has a thickness of 0.134 cm. How many CD’s are needed to form a stack of CD’sEXACTLY 1 mile high (1 mile=5280 ft., 1ft= 12 in, 1 in = 2.54 cm)?1
Three Important LawsLaw of conservation of mass (Lavoisier):Mass is neither created nor destroyed in a chemical reactionLaw of definite proportion (Proust):A given compound always contains exactly the same proportion of elements bymassLaw of multiple proportions (Dalton):When two elements form a series of compounds, the ratios of the masses of thesecond element that combine with 1 gram of the first element can always bereduced to small whole numbersSection 2.3 – Dalton’s Atomic TheoryDalton’s Atomic Theory (1808)Each element is made up of tiny particles called atomsThe atoms of a given element are identical; the atoms of different elements are differentin some fundamental way or waysChemical compounds are formed when atoms of different elements combine with eachother. A given compound always has the same relative numbers and types of atoms.Chemical reactions involved reorganization of the atoms—changes in the way they arebound togetherThe atoms themselves are not changed in a chemical reactionGay-Lussac and Avogadro (1809-1811)Gay-LussacMeasured (under same conditions of T and P) the volumes of gases that reactedwith each otherAvogadro’s HypothesisAt the same T and P, equal volumes of different gases contain the same number ofparticlesVolume of a gas is determined by the number, not the size, of moleculesRepresenting Gay—Lussac’s ResultsSection 2.4 – Early Experiments to Characterize the Atom2
J.J. Thomson (1898-1903)Postulated the existence of negatively charged particles, that we now call electrons, using

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