BB Chap. 2 - Atoms, Ions and Molecules The Building Blocks of Matter McWF18.pptx

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Atoms, Ions andMolecules: TheBuilding Blocks ofMatterChapter 2
Atomic TheoryAtoms are the fundamental building blocks(smallest particles) of matter.Model is consistent with observation (laws) andexplains behavior of matter.
First Evidence of AtomsJ.L. Proust: Law of Definite ProportionsCompounds always contain the same proportions oftheir component elements.J. Dalton: Law of Multiple ProportionsWhen two elements combine to make two (or more)compounds, the ratio of the masses of the first element, whichcombine with a given mass of the second element, is a ratio ofsmall whole numbers.(SnO) 11.9% O/88.1% Sn = 0.135(SnO2) 21.3% O/78.7% Sn = 0.2710.271/0.135 is very close to 2:1
Atomic TheoryDalton concluded that elements combinedaccording to the law of multiple proportionsbecause they were composed of atoms.Dalton’sAtomic Theoryproposed that atomswere the smallest units of matter, but…..By the end of the 19thcentury, scientist began tosuspect that atoms were made up of evensmaller subatomic particles.
Charge/Mass Ratio ofElectronCathode Ray Tube ExperimentJ. J. ThomsonThomson learned:Rays are negatively charged particlesCharge/Mass ratio same forallcathodes (i.e.allelements)Electrons are present in all elementse/m =1.75882028 x 108C/g
Charge and Mass ofElectronOil Drop ExperimentRobert MillikanDetermined charge of anelectron.Charge:1.602 x 1019CC is coulombsCalculated mass usingThompson’s e/m ratioMass:9.10938 x 1028g
Structure of the AtomPlum Pudding Model(Thomson)The atom contains manynegatively charged electronsheld in the atom by theirattraction for a positivelycharged electric field withinthe atom.Mass of atom is spread acrossits entire volume.
RadioactivityBeta (b) particles: a radioactive emissionthat is a high-energy electron.Alpha (a) particle: a radioactive emissionwith a charge of 2+ and a mass equivalentto that of a helium nucleus.
Structure of the Atom:Nucleus_______________: Gold Foil ExperimentRutherford concluded:Atoms are mostly ______________.Atoms have a _____________________containing all of theatom’s positive charge and most of the mass
Discovery of the ProtonRutherford and others bombarded elements witha particlesObservation: Bombarding elements with aparticles changed, or transmuted, them into otherelementsHydrogen atom nuclei, also known as protonswere frequently produced in these experimentsScientist realized that hydrogen nuclei were apart of all nuclei
NeutronsJames Chadwick detected andcharacterized free neutrons
Structure of the Atom

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