Chapter 2 Atoms, Molecules and Ions 6 Slides.pdf - 1/7/2019...

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1/7/20191Chapter 2Atoms, Molecules and Ions© Eric L. Johnson, 2019Dalton’s First Postulate1)Each elementis composedof extremelysmall particlescalled atoms.2Dalton’s Second Postulate2) All atoms of agiven element areidentical, but theatoms of oneelement aredifferent from theatoms of all otherelements.3Dalton’s Third Postulate3)Atoms of oneelement cannot bechanged intoatoms of adifferent elementby chemicalreactions; atomsare neither creatednor destroyed inchemical reactions.4Law of Conservation of MassThe total mass ofmaterials present aftera chemical reaction isthe same as the totalmass present before thereaction.5Dalton’s Fourth Postulate4)Compounds areformed whenatoms of morethan one elementcombine; a givencompound alwayshas the samerelative numberand kind ofatoms.6
1/7/20192The ElectronStreams of negatively charged particles were found to emanatefrom cathode tubes, causing fluorescence.J. J. Thomson is credited with their discovery (1897).7The Atom, circa 1900The prevailing theorywas that of the “plumpudding” model, putforward by Thomson.It featured a positivesphere of matter withnegative electronsimbedded in it.8Discovery of the NucleusErnest Rutherfordshotparticles ata thin sheet ofgold foil andobserved thepattern of scatterof the particles.9The Nuclear AtomRutherford postulated avery small, dense nucleuswith the electrons aroundthe outside of the atom.Most of the volume of theatom is empty space.Other subatomic particles(protons and neutrons)were discovered.

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