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CHEM 1610 (2)
Chapter 2

The Components of Matter - Chapter 2 Notes

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CHEM 1610
Mike Mohajeri

21Substancetype of matter element or compound with a fixed compositionoElementsimplest type of substance with unique physical and chemical properties consisting of one kind of atomMoleculestructure consisting of two or more atoms that are bound chemically and behave as an independent unitoCompoundsubstance composed of two or more elements that are chemically combined in fixed proportionsProperties different than those of its elementsMixturetwo or more elements andor compounds that are physically intermingledoNot chemically bound22Law of mass conservationthe total mass of substances does not change during a chemical reactionoOnly number of substances and properties may changeLaw of definite constant compositiona particular compound is composed of the same elements in the same parts fractions by mass regardless of its sourceoFraction by mass mass fractionportion of a compounds mass contributed by an elementoPercent by massfraction by mass expressed as a percentLaw of multiple proportionsif elements A and B react to form two or more compounds the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbersoThe same two elements can form more than one compound ie carbon oxide I and II and carbon oxide II has 2x more carbon than carbon I23Daltons atomic theoryoAll matter is composed of atoms that cannot be created or destroyedoAtoms of one element cannot be converted into atoms of another elementoAtoms of an element all have the same mass and properties which are different from atoms of any other elementoCompounds form from specific ratios of atoms of different elementsMass lawsoMass conservationatoms cannot be created destroyed or converted into other types of atomsoDefinite compositioncompounds are combinations of specific ratios of different atoms each of which has a particular massoMultiple proportionsthe masses of B that combine with a fixed mass of A gives asmall wholenumber ratio because different numbers of B atoms combine with each A atom in different compoundsEx carbon oxide I CO and carbon oxide II CO224Discovery of electronsoMasscharge ratioJJ ThomsonMeasured the ratio of a cathode ray particle to its charge and discovered that it was lighter than an atomoChargeRobert MillikanObserved the movement of oil droplets in an electrically charged apparatus measured the mass of the droplets based on their rate of fall measured the charge based on the strength of the magnetic field required to suspend the droplets3128Mass of electron9109 x 10 kg9109 x 10 gDiscovery of the nucleus and protonsErnest RutherfordAimed a beam of alpha particles at gold foil most went straight through no deflection some deflected slightly protons some deflected greatly neutronsConcluded that there must be a small dense positive particleNamed protonsDiscovery of neutronsJames Chadwick25Atomelectrically neutral spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electronsoProton pfound in the nucleus positively charged0oNeutron nfound in the nucleus uncharged mass slightly greater than that of a protonoElectron eoccupies the space around the nucleus negatively chargedProperties of the Three Subatomic Particles
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