Chapter 4Chapter 4“Atomic Structure”“Atomic Structure”Pre-AP ChemistryPre-AP ChemistryCharles Page High SchoolCharles Page High SchoolStephen L. CottonStephen L. Cotton
Section 4.1 Defining the AtomSection 4.1 Defining the AtomOBJECTIVES:OBJECTIVES:DescribeDescribe Democritus’s ideasDemocritus’s ideasabout atoms.about atoms.
Section 4.1 Defining the AtomSection 4.1 Defining the AtomOBJECTIVES:OBJECTIVES:ExplainExplain Dalton’s atomicDalton’s atomictheory.theory.
Section 4.1 Defining the AtomSection 4.1 Defining the AtomOBJECTIVES:OBJECTIVES:IdentifyIdentify what instrument iswhat instrument isused to observe individualused to observe individualatoms.atoms.
Section 4.1 Defining the AtomSection 4.1 Defining the Atom The Greek philosopherThe Greek philosopher DemocritusDemocritus (460(460B.C.B.C. – 370– 370 B.CB.C.) was among the first to.) was among the first tosuggest the existence of atoms (fromsuggest the existence of atoms (fromthe Greek word “atomos”)the Greek word “atomos”) He believed that atoms wereHe believed that atoms were indivisibleindivisible andandindestructibleindestructible His ideas did agree with later scientificHis ideas did agree with later scientifictheory, but did not explain chemicaltheory, but did not explain chemicalbehavior, and wasbehavior, and was not based on thenot based on thescientific methodscientific method – but just philosophy– but just philosophy
Dalton’s Atomic TheoryDalton’s Atomic Theory (experiment based!)(experiment based!)3) Atoms of different elements combine insimple whole-number ratios to formchemical compounds4) In chemical reactions, atoms are combined,separated, or rearranged – but neverchanged into atoms of another element.1) All elements are composed oftiny indivisible particles calledatoms2) Atoms of the same element areidentical. Atoms of any oneelement are different fromthose of any other element.John Dalton(1766 – 1844)
Sizing up the AtomSizing up the Atom Elements are able to be subdivided intosmaller and smaller particles – these arethe atoms, and they still have propertiesof that elementIf you could line up 100,000,000copper atoms in a single file, theywould be approximately 1 cm longDespite their small size, individualatoms are observable with instrumentssuch as scanning tunneling (electron)microscopes
Section 4.2Section 4.2Structure of the Nuclear AtomStructure of the Nuclear AtomOBJECTIVES:OBJECTIVES:IdentifyIdentify three types ofthree types ofsubatomic particles.subatomic particles.
Section 4.2Section 4.2Structure of the Nuclear AtomStructure of the Nuclear AtomOBJECTIVES:OBJECTIVES:DescribeDescribe the structure ofthe structure ofatoms, according to theatoms, according to theRutherford atomic model.Rutherford atomic model.
Section 4.2Section 4.2Structure of the Nuclear AtomStructure of the Nuclear Atom One change to Dalton’s atomicOne change to Dalton’s atomictheory is thattheory is that atoms are divisibleatoms are divisibleinto subatomic particles:into subatomic particles: Electrons, protons, and neutronsElectrons, protons, and neutrons areareexamples of these fundamentalexamples of these fundamentalparticlesparticles There are many other types ofThere are many other types ofparticles, but we will study these threeparticles, but we will study these three
Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode raytube to deduce the presence of a negativelycharged particle: the electron
ModernModern CCathodeathode RRayay TTubesubesCathode ray tubes pass electricitythrough a gas that is contained at avery low pressure.Television Computer Monitor
Mass of the ElectronMass of the Electron1916 – Robert Millikan determines the massof the electron: 1/1840 the mass of ahydrogen atom; has one unit of negativechargeThe oil drop apparatusMass of theelectron is9.11 x 10-28g
Conclusions from the StudyConclusions from the Studyof the Electron:of the Electron:a) Cathode rays have identical propertiesregardless of the element used toproduce them. All elements must containidentically charged electrons.b) Atoms are neutral, so there must bepositive particles in the atom to balancethe negative charge of the electronsc) Electrons have so little mass that atomsmust contain other particles that accountfor most of the mass
Conclusions from the StudyConclusions from the Studyof the Electron:of the Electron: Eugen Goldstein in 1886 observedwhat is now called the “proton” -particles with a positive charge, anda relative mass of 1 (or 1840 timesthat of an electron) 1932 – James Chadwick confirmedthe existence of the “neutron” – aparticle with no charge, but a massnearly equal to a proton
Subatomic ParticlesSubatomic ParticlesParticleParticle ChargeCharge Mass (g)Mass (g) LocationLocationElectronElectron(e(e--)) -1-1 9.11 x 109.11 x 10-28-28 ElectronElectroncloudcloudProtonProton(p(p++)) +1+1 1.67 x 101.67 x 10-24-24NucleusNucleusNeutronNeutron(n(noo)) 00 1.67 x 101.67 x 10-24-24NucleusNucleus
Thomson’s Atomic ModelThomson’s Atomic ModelThomson believed that the electronswere like plums embedded in apositively charged “pudding,” thus itwas called the “plum pudding” model.J. J. Thomson
Ernest Rutherford’sErnest Rutherford’sGold Foil Experiment - 1911Gold Foil Experiment - 1911 Alpha particles are helium nuclei -The alpha particles were fired at a thinsheet of gold foil Particles that hit on the detectingscreen (film) are recorded
Rutherford’s problem:Rutherford’s problem:In the following pictures, there is a targethidden by a cloud. To figure out the shape ofthe target, we shot some beams into the cloudand recorded where the beams came out. Canyou figure out the shape of the target?Target#1Target#2
Rutherford’s FindingsRutherford’s Findingsa) The nucleus is smallb) The nucleus is densec) The nucleus is positivelycharged Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected“Like howitzer shells bouncingoff of tissue paper!”Conclusions:
The Rutherford Atomic ModelThe Rutherford Atomic Model Based on his experimental evidence:Based on his experimental evidence: The atom is mostly empty spaceThe atom is mostly empty space All the positive charge, and almost allAll the positive charge, and almost allthe mass is concentrated in a small areathe mass is concentrated in a small areain the center. He called this a “in the center. He called this a “nucleusnucleus”” The nucleus is composed of protonsThe nucleus is composed of protonsand neutrons (theyand neutrons (they makemake the nucleus!)the nucleus!) The electrons distributed around theThe electrons distributed around thenucleus, and occupy most of the volumenucleus, and occupy most of the volume His model was called a “His model was called a “nuclear modelnuclear model””
Section 4.3Section 4.3Distinguishing Among AtomsDistinguishing Among AtomsOBJECTIVES:OBJECTIVES:ExplainExplain what makeswhat makeselementselements andand isotopesisotopesdifferent from each other.different from each other.
Section 4.3Section 4.3Distinguishing Among AtomsDistinguishing Among AtomsOBJECTIVES:OBJECTIVES:CalculateCalculate the number ofthe number ofneutrons in an atom.neutrons in an atom.
Section 4.3Section 4.3Distinguishing Among AtomsDistinguishing Among AtomsOBJECTIVES:OBJECTIVES:CalculateCalculate the atomic mass ofthe atomic mass ofan element.an element.
Section 4.3Section 4.3Distinguishing Among AtomsDistinguishing Among AtomsOBJECTIVES:OBJECTIVES:ExplainExplain why chemists usewhy chemists usethe periodic table.the periodic table.
Atomic NumberAtomic Number Atoms are composed ofAtoms are composed of identicalidenticalprotons, neutrons, and electronsprotons, neutrons, and electrons How then are atoms of one elementHow then are atoms of one elementdifferent from another element?different from another element? Elements are different because theyElements are different because theycontain different numbers ofcontain different numbers of PROTONSPROTONS The “The “atomic numberatomic number” of an element is” of an element isthethe number of protonsnumber of protons in the nucleusin the nucleus # protons in an atom = # electrons# protons in an atom = # electrons
Atomic NumberAtomic NumberAtomic number (Z) of an element isthe number of protons in the nucleusof each atom of that element.ElementElement # of protons# of protons Atomic # (Z)Atomic # (Z)CarbonCarbon 66 66PhosphorusPhosphorus 1515 1515GoldGold 7979 7979
Mass NumberMass NumberMass number is the number of protonsand neutrons in the nucleus of anisotope: Mass # = p++ n0NuclideNuclide pp++nn00ee-- Mass #Mass #OxygenOxygen -- 1010-- 3333 4242-- 3131 15158 8 1818Arsenic 75 33 75Phosphorus 15 3116
Complete SymbolsComplete Symbols Contain the symbol of the element,Contain the symbol of the element,the mass number and the atomicthe mass number and the atomicnumber.number.XMassnumberAtomicnumberSubscript →Superscript →
SymbolsSymbolsFind each of these:Find each of these:a)a) number of protonsnumber of protonsb)b) number ofnumber ofneutronsneutronsc)c) number ofnumber ofelectronselectronsd)d) Atomic numberAtomic numbere)e) Mass NumberMass NumberBr8035
SymbolsSymbolsIf an element has an atomicIf an element has an atomicnumber of 34 and a massnumber of 34 and a massnumber of 78, what is the:number of 78, what is the:a)a) number of protonsnumber of protonsb)b) number of neutronsnumber of neutronsc)c) number of electronsnumber of electronsd)d) complete symbolcomplete symbol
SymbolsSymbolsIf an element has 91If an element has 91protons and 140 neutronsprotons and 140 neutronswhat is thewhat is thea)a) Atomic numberAtomic numberb)b) Mass numberMass numberc)c) number of electronsnumber of electronsd)d) complete symbolcomplete symbol
SymbolsSymbolsIf an element has 78If an element has 78electrons and 117 neutronselectrons and 117 neutronswhat is thewhat is thea)a) Atomic numberAtomic numberb)b) Mass numberMass numberc)c) number of protonsnumber of protonsd)d) complete symbolcomplete symbol
IsotopesIsotopes Dalton was wrong about allDalton was wrong about allelements of the same typeelements of the same typebeing identicalbeing identical Atoms of the same elementAtoms of the same element cancanhave different numbers ofhave different numbers ofneutronsneutrons.. Thus, different mass numbers.Thus, different mass numbers. These are calledThese are called isotopesisotopes..
IsotopesIsotopes Frederick SoddyFrederick Soddy (1877-1956)(1877-1956)proposed the idea of isotopes inproposed the idea of isotopes in19121912 Isotopes are atoms of the same elementhaving different masses, due to varyingnumbers of neutrons. Soddy won the Nobel Prize inSoddy won the Nobel Prize inChemistry in 1921 for his work withChemistry in 1921 for his work withisotopes and radioactive materials.isotopes and radioactive materials.
Naming IsotopesNaming IsotopesWe can also put the massWe can also put the massnumbernumber afterafter the name of thethe name of theelement:element:carbon-12carbon-12carbon-14carbon-14uranium-235uranium-235
Isotopes are atoms of the same element havingdifferent masses, due to varying numbers ofneutrons.IsotopeIsotope ProtonsProtons ElectronsElectrons NeutronsNeutrons NucleusNucleusHydrogen–1Hydrogen–1(protium)(protium) 11 11 00Hydrogen-2Hydrogen-2(deuterium)(deuterium) 11 11 11Hydrogen-3Hydrogen-3(tritium)(tritium)11 11 22
IsotopesIsotopesElementsoccur innature asmixtures ofisotopes.Isotopes areatoms of thesame elementthat differ inthe number ofneutrons.
Atomic MassAtomic Mass How heavy is an atom of oxygen?How heavy is an atom of oxygen? It depends, because there are differentIt depends, because there are differentkindskinds of oxygen atoms.of oxygen atoms. We are more concerned with theWe are more concerned with the averageaverageatomic mass.atomic mass. This is based on the abundanceThis is based on the abundance(percentage) of each variety of that(percentage) of each variety of thatelement in nature.element in nature. We don’t use grams for this mass becauseWe don’t use grams for this mass becausethe numbers would be too small.the numbers would be too small.
Measuring Atomic MassMeasuring Atomic Mass Instead of grams, the unit we useInstead of grams, the unit we useis theis the Atomic Mass UnitAtomic Mass Unit (amu)(amu) It is defined as one-twelfth theIt is defined as one-twelfth themass of a carbon-12 atom.mass of a carbon-12 atom.Carbon-12 chosen because of itsCarbon-12 chosen because of its isotope purityisotope purity.. Each isotope has its own atomicEach isotope has its own atomicmass, thus we determine themass, thus we determine theaverage from percent abundance.average from percent abundance.
To calculate the average:To calculate the average:Multiply the atomic mass ofMultiply the atomic mass ofeach isotope by it’seach isotope by it’sabundance (expressed as aabundance (expressed as adecimal), then add thedecimal), then add theresults.results. If not told otherwise, the mass of theIf not told otherwise, the mass of theisotope is expressed inisotope is expressed in atomic massatomic massunitsunits (amu)(amu)
Atomic MassesAtomic MassesIsotopeIsotope SymbolSymbol Composition ofComposition ofthe nucleusthe nucleus% in nature% in natureCarbon-12Carbon-12 1212CC 6 protons6 protons6 neutrons6 neutrons98.89%98.89%Carbon-13Carbon-13 1313CC 6 protons6 protons7 neutrons7 neutrons1.11%1.11%Carbon-14Carbon-14 1414CC 6 protons6 protons8 neutrons8 neutrons<0.01%<0.01%Atomic mass is the average of all thenaturally occurring isotopes of thatelement.Carbon = 12.011
The Periodic Table:The Periodic Table:A PreviewA Preview A “periodic table” is anarrangement of elements in whichthe elements are separated intogroups based on a set of repeatingpropertiesThe periodic table allows you toeasily compare the properties ofone element to another
The Periodic Table:The Periodic Table:A PreviewA Preview Each horizontal row (there are 7 ofthem) is called a periodEach vertical column is called agroup, or familyElements in a group have similarchemical and physical propertiesIdentified with a number andeither an “A” or “B”More presented in Chapter 6