Post on 21-Jan-2016
Chapter 4Chapter 4Atomic Atomic
StructureStructurep. 101p. 101
Section 4.1 Defining the AtomSection 4.1 Defining the Atom Greek philosopher Greek philosopher DemocritusDemocritus
suggested atoms (Greek suggested atoms (Greek “atomos”)“atomos”) Believed Believed indivisibleindivisible & &
indestructibleindestructible His ideas His ideas
Based on philosophyBased on philosophy didn’t explain chem behaviordidn’t explain chem behavior Lacked experimental support Lacked experimental support
Dalton’s Atomic TheoryDalton’s Atomic Theory (experiment based!) (experiment based!)
3) Atoms of diff elements combine in simple whole # ratios (chem cmpds)
4) In chem rxns, atoms combine, separate, or rearrange – never change into atoms of another element
1) All elements composed of indivisible particles (atoms)
2) Atoms of same element identical. Atoms of 1 different from other elements
John Dalton(1766 – 1844)
Sizing up the AtomSizing up the Atom Elements subdivided into smaller particles – atoms,… still have properties of that element
Line up 1.0 x 108 copper atoms = 1 cm longindividual atoms observed w/ scanning tunneling (electron) microscopes
The atom 1:15
Section 4.2Section 4.2Structure of the Nuclear AtomStructure of the Nuclear Atom
One change to Dalton’s atomic One change to Dalton’s atomic theory - theory - atoms ARE divisibleatoms ARE divisible
Into subatomic particles:Into subatomic particles:
Electrons, protons, and Electrons, protons, and neutronsneutrons
Discovery of ElectronDiscovery of Electron1897 - J.J. Thomson used cathode ray tube to deduce presence of negatively charged
particle…….electronelectron
JJ Thomson’s Cathode Ray 2:49
Mass of ElectronMass of Electron
1916 – Robert Millikan determines e- mass: 1/1840 mass of H atom; one unit of - charge
The oil drop apparatus
Mass of the electron is 9.11 x 10-28 g
Conclusions from the Study Conclusions from the Study of the Electron:of the Electron:
a) All elements must contain identically charged e-s.
b) Atoms r neutral, must be + particles to balance – e-s
c) e-s have little mass - atoms must contain other more massive particles
Conclusions from Electron Conclusions from Electron Study:Study:
1932 – James Chadwick confirmed “neutron” existence
particle w/ no chargen0 mass = p+ mass
Subatomic ParticlesSubatomic Particles
ParticleParticle ChargeCharge Mass (g)Mass (g) LocationLocation
ElectronElectron
(e(e--)) 1-1- 9.11 x 109.11 x 10-28-28 Electron Electron cloudcloud
ProtonProton (p(p++)) 1+1+ 1.67 x 101.67 x 10-24-24 NucleusNucleus
NeutronNeutron
(n(noo)) 00 1.67 x 101.67 x 10-24-24 NucleusNucleus
Thomson’s Atomic ModelThomson’s Atomic Model
Believed e-s like plums in + charged “pudding,” ----- “plum pudding” model.
J. J. Thomson
Ernest Rutherford’sErnest Rutherford’sGold Foil Experiment - 1911Gold Foil Experiment - 1911
massive alpha particles (He atom w/o e-’s) fired at Au foilThought most would pass thru w/ slight deflectionMOST passed straight thru!
Rutherford’s Gold Foil Experiment 4:06
Rutherford’s problem:Rutherford’s problem:In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?
Target #1
Target #2
The Answers:The Answers:
Target #1 Target #2
Rutherford’s FindingsRutherford’s Findings Most particles passed thru Few deflected VERY FEW greatly deflected
The Atom The Atom SongSong
Atoms song - Mark Rosengarten
“As incredible as howitzer shells bouncing off of tissue paper!”
The Rutherford Atomic ModelThe Rutherford Atomic Model New theory:New theory:
atom mostly empty spaceatom mostly empty space NucleusNucleus
pp++ & n & n00 m makeake nucleus! nucleus!all + chargeall + chargealmost all massalmost all mass
e-s around nucleus…occupy most e-s around nucleus…occupy most volumevolume
called “called “nuclear modelnuclear model””
Rutherford’s Atom 3:08
Quarks 2:56
Section 4.3Section 4.3Distinguishing Among Atoms Distinguishing Among Atoms
p. 110p. 110
How are elements different How are elements different from one another?from one another?
different # different # p+’s!p+’s! ID’s elements (like fingerprint/DNA)ID’s elements (like fingerprint/DNA)
Atomic NumberAtomic NumberAtomic number (Z) of element = # of p+’s in nucleus of each atom of that of that element.element.
ElementElement # of protons# of protons Atomic # (Z)Atomic # (Z)
CarbonCarbon 66
PhosphorusPhosphorus 1515
GoldGold 7979
615
79
Mass NumberMass Number
Mass number is # of p+’s and n0’s in nucleus of isotope:
nn0 0 = mass # - atomic = mass # - atomic ## pp++ nn00 ee-- Mass #Mass #
Oxygen Oxygen - - 1010
- - 3333 4242
- - 3131 1515
8 8 1818
Arsenic 75 33 75
Phosphorus 15 3116
Complete SymbolsComplete Symbols
X Massnumber
Atomicnumber
Subscript →
Superscript →
SymbolsSymbols Identify each of these: Identify each of these:
a)a) number of protonsnumber of protons
b)b) number of neutronsnumber of neutrons
c)c) number of electronsnumber of electrons
d)d) Atomic numberAtomic number
e)e) Mass NumberMass Number
Br80 35
Practice…..Practice….. If an element has an atomic If an element has an atomic
number of 34 and a mass number of 34 and a mass number of 78, what is the: number of 78, what is the:
a)a) number of protonsnumber of protons
b)b) number of neutronsnumber of neutrons
c)c) number of electronsnumber of electrons
d)d) complete symbolcomplete symbol
More practice…….More practice……. If an element has 91 If an element has 91
protons and 140 neutrons protons and 140 neutrons what is the what is the
a)a) Atomic numberAtomic number
b)b) Mass numberMass number
c)c) number of electronsnumber of electrons
d)d) complete symbolcomplete symbol
IsotopesIsotopes
Dalton was wrong!Dalton was wrong!Atoms of same elements NOT Atoms of same elements NOT
identical…identical…cancan have different # have different # nn00’s’s..
different mass #different mass #Isotopes Isotopes
(flavors)(flavors)
IsotopesIsotopes Frederick SoddyFrederick Soddy
proposed idea of isotopes proposed idea of isotopes in 1912in 1912 1921 Nobel Prize in Chemistry 1921 Nobel Prize in Chemistry crater w/ his name on far side of crater w/ his name on far side of
MoonMoon
Isotopes - atoms of same element w/ diff masses b/c varying #s of n0
Elements occur in nature as Elements occur in nature as mixturesmixtures of of isotopes.isotopes.
Naming IsotopesNaming Isotopes
put mass # put mass # afterafter element element name:name:carbon-12 carbon-12 fluorine-19fluorine-19uranium-235uranium-235
IsotopeIsotope ProtonsProtons ElectronsElectrons NeutronsNeutrons NucleusNucleus
Hydrogen–1Hydrogen–1
(protium)(protium) 11 11 00
Hydrogen-2Hydrogen-2
(deuterium)(deuterium) 11 11 11
Hydrogen-3Hydrogen-3
(tritium)(tritium)
11 11 22
Atomic MassAtomic Mass How heavy is an oxygen atom?How heavy is an oxygen atom?
Depends, b/c different Depends, b/c different kindskinds of oxygen of oxygen atoms exist.atoms exist.
average average atomic massatomic mass Based on abundance (%) of each variety Based on abundance (%) of each variety
of that element in nature.of that element in nature. not in grams - #’s tooooo smallnot in grams - #’s tooooo small
Measuring Atomic MassMeasuring Atomic Mass
Atomic Mass UnitAtomic Mass Unit (amu)(amu) 1/12 mass of C-12 atom1/12 mass of C-12 atom
C-12 b/c C-12 b/c isotope purityisotope purity Each isotope has own atomic mass Each isotope has own atomic mass determine average from % abundancedetermine average from % abundance
To calculate weighted To calculate weighted average mass:average mass:
Atomic massAtomic mass xx isotope isotope abundance (change % to abundance (change % to decimal)decimal)
Add all resultsAdd all results Isotope mass usually in Isotope mass usually in amuamu’s’s
Atomic MassesAtomic Masses
IsotopeIsotope SymbolSymbol Composition Composition of the nucleusof the nucleus
% in nature% in nature
Carbon-Carbon-1212
1212CC 6 protons6 protons
6 neutrons6 neutrons
98.89%98.89%
Carbon-Carbon-1313
1313CC 6 protons6 protons
7 neutrons7 neutrons
1.11%1.11%
Carbon-Carbon-1414
1414CC 6 protons6 protons
8 neutrons8 neutrons
<0.01%<0.01%
Atomic mass - avg of all naturally occurring isotopes of that element
12.01What is the average atomic mass of Carbon?What is the average atomic mass of Carbon?
Atomic Atomic mass mass (amu)(amu)
12
13.00
14.00
- Page 117
Question
Solution
Answer
Knowns and Unknown