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Atomos: Not to Be CutAtomos: Not to Be Cut
The History of Atomic TheoryThe History of Atomic Theory
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ATOMIC THEORYATOMIC THEORY
a theory of the nature of matter. Ita theory of the nature of matter. It
states that all matter is composed ofstates that all matter is composed ofatoms. It is credited to John Daltonatoms. It is credited to John Dalton
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Atomic ModelsAtomic Models
This model of theThis model of theatom may looatom may loofamiliar to you. This isfamiliar to you. This isthe !ohr model. Inthe !ohr model. In
this model" thethis model" thenucleus is or#ited #ynucleus is or#ited #yelectrons" $hich areelectrons" $hich arein different ener%yin different ener%y
le&els.le&els. A model uses familiar ideas toA model uses familiar ideas to
e'plain unfamiliar factse'plain unfamiliar factso#ser&ed in nature.o#ser&ed in nature. A model can #e chan%ed asA model can #e chan%ed as
ne$ information is collected.ne$ information is collected.
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The atomic modelThe atomic modelhas chan%edhas chan%edthrou%hout thethrou%hout the
centuries" startin%centuries" startin%in ()) !C" $hen itin ()) !C" $hen it
looed lielooed lie aa
#illiard #all#illiard #all **
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+ho are these men,+ho are these men,
In this lesson" $e-ll learn
a#out the men $hose uests
for no$led%e a#out the
fundamental nature of the
uni&erse helped define our
&ie$s.
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DemocritusDemocritus
This is the /reeThis is the /ree
philosopher Democritusphilosopher Democritus
$ho #e%an the search for$ho #e%an the search for
a description of mattera description of matter
more thanmore than 0())0())years a%o.years a%o. He ased1 Could matterHe ased1 Could matter
#e di&ided into smaller#e di&ided into smaller
and smaller piecesand smaller pieces
fore&er" or $as there afore&er" or $as there alimitlimitto the num#er ofto the num#er of
times a piece of mattertimes a piece of matter
could #ecould #e di&ideddi&ided,,
400 BC
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AtomosAtomos
His theory1 Matter could notHis theory1 Matter could not
#e di&ided into smaller and#e di&ided into smaller and
smaller pieces fore&er"smaller pieces fore&er"
e&entually the smalleste&entually the smallest
possi#le piece $ould #epossi#le piece $ould #e
o#tained.o#tained.
This piece $ould #eThis piece $ould #e
indi&isi#le.indi&isi#le.
He named the smallestHe named the smallest
piece of matter 2atomos"3piece of matter 2atomos"3
meanin% 2not to #e cut.3meanin% 2not to #e cut.3
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AtomosAtomos
To Democritus" atomsTo Democritus" atoms
$ere$ere smallsmall" hard" hard
particles that $ere allparticles that $ere all
made of the samemade of the same
material #ut $erematerial #ut $ere
differentdifferentshapes andshapes and
si4es.si4es.
Atoms $ereAtoms $ere infiniteinfiniteininnum#er" al$ays mo&in%num#er" al$ays mo&in%
and capa#le of 5oinin%and capa#le of 5oinin%
to%ether.to%ether.
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This theory wasThis theory was
ignored and forgottenignored and forgotten
for more thanfor more than20002000
years!years!
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+hy,+hy,
The eminentThe eminentphilosophersphilosophers
of the time,of the time,
AristotleAristotleandand
Plato, had aPlato, had amoremore
respected,respected,
(and ultimately(and ultimately
wrongwrong) theory.) theory.
Aristotle and 6lato fa&ored the earth, fire, air
and water approach to the nature of matter.Their ideas held s$ay #ecause of their
eminence as philosophers. The atomosidea
$as #uried for appro'imately 0))) years.
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Dalton-s ModelDalton-s Model
In the early 78))s"In the early 78))s"
the En%lishthe En%lish
Chemist JohnChemist John
DaltonDalton performed aperformed a
num#er ofnum#er of
e'periments thate'periments that
e&entually led toe&entually led tothe acceptance ofthe acceptance of
the idea of atoms.the idea of atoms.
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Dalton-s TheoryDalton-s Theory
He deduced that allHe deduced that all
elementselementsare composed ofare composed of
atoms. Atoms areatoms. Atoms are
indi&isi#le andindi&isi#le and
indestructi#le particles.indestructi#le particles. Atoms of theAtoms of the samesameelementelement
are e'actly alie.are e'actly alie.
Atoms ofAtoms of differentdifferentelementselements
areare differentdifferent..
CompoundsCompoundsare formed #yare formed #y
the 5oinin% of atoms of t$othe 5oinin% of atoms of t$o
or more elements.or more elements.
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..
This theoryThis theory
became onebecame one
of theof thefoundationsfoundations
of modernof modernchemistry.chemistry.
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Thomson-s 6lum 6uddin% ModelThomson-s 6lum 6uddin% Model
InIn 789:789:" the" the
En%lish scientistEn%lish scientist
J.J. ThomsonJ.J. Thomsonpro&ided the firstpro&ided the first
hint that an atomhint that an atom
is made of e&enis made of e&ensmallersmallerparticles.particles.
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Thomson ModelThomson Model
He proposed a modelHe proposed a modelof the atom that isof the atom that issometimes called thesometimes called the226lum6lum6uddin%6uddin%33
model.model.Atoms $ere madeAtoms $ere made
from a positi&elyfrom a positi&elychar%edchar%edsu#stancesu#stance
$ith ne%ati&ely$ith ne%ati&elychar%ed electronschar%ed electronsscatteredscattereda#out" liea#out" lieraisins in a puddin%.raisins in a puddin%.
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Thomson ModelThomson Model
Thomson studiedThomson studiedthethe passa%epassa%e of anof anelectric currentelectric current
throu%h a %as.throu%h a %as.As the currentAs the current
passed throu%hpassed throu%hthe %as" it %aðe %as" it %a&eoff rays ofoff rays ofne%ati&elyne%ati&elychar%ed particles.char%ed particles.
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Thomson ModelThomson Model
This surprisedThis surprised
Thomson"Thomson"
#ecause the#ecause theatoms of the %asatoms of the %as
$ere unchar%ed.$ere unchar%ed.
+here had the+here had thene%ati&e char%esne%ati&e char%es
come from,come from,
+here did
they comefrom,
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Thomson concluded that the
ne%ati&e char%es came from within
the atom.
A particle smaller than an atom had
to e'ist.
The atom $as di&isi#le;
Thomson called the ne%ati&elychar%ed 2corpuscles"3 today no$n
as electrons.
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= 0))) the mass of the hydro%en atomatom
Discovery of the ElectronDiscovery of the Electron1909 R.A Millikan1909 R.A Millikan
m = 9.11 10-31kg
e = -1.010-19 !
Also confirmed and estimated the negative electric
charge on an electron
http://education.jlab.org/atomtour/fact2.htmlhttp://education.jlab.org/atomtour/fact2.htmlhttp://education.jlab.org/atomtour/fact2.htmlhttp://education.jlab.org/atomtour/fact2.htmlhttp://../zMovies/e)%20millikan%20oil%20drop.mov7/24/2019 1 - History of Atomic Theory
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Rutherford-s /old ?oilRutherford-s /old ?oil
E'perimentE'periment In 79)8" the En%lishIn 79)8" the En%lishphysicist Ernestphysicist Ernest
Rutherford $as hardRutherford $as hard
at $or on anat $or on ane'periment thate'periment that
seemed to ha&e littleseemed to ha&e little
to do $ith unra&elin%to do $ith unra&elin%
the mysteries of thethe mysteries of the
atomic structure.atomic structure.
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Rutherford-s e'periment In&ol&edRutherford-s e'periment In&ol&edfirin% a stream of tinyfirin% a stream of tiny positi&elypositi&elychar%edchar%edparticles at a thin sheet ofparticles at a thin sheet of%old foil%old foil@0))) atoms thic@0))) atoms thic
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MostMostof the positi&elyof the positi&elychar%ed 2#ullets3 passedchar%ed 2#ullets3 passedri%ht throu%h the %oldri%ht throu%h the %oldatoms in the sheet ofatoms in the sheet of %old%old
foilfoil$ithout chan%in%$ithout chan%in%course at all.course at all.
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This could only mean that the %old atoms in theThis could only mean that the %old atoms in thesheet $ere mostlysheet $ere mostly open spaceopen space. Atoms $ere. Atoms $ere notnota puddin% filled $ith a positi&ely char%eda puddin% filled $ith a positi&ely char%edmaterial.material.
Rutherford concluded that an atom had aRutherford concluded that an atom had a small"small"dense" positi&ely char%ed centerdense" positi&ely char%ed centerthatthat repelledrepelledhis positi&ely char%ed 2#ullets.3his positi&ely char%ed 2#ullets.3
He called the center of the atom the 2He called the center of the atom the 2nucleusnucleus33 The nucleus isThe nucleus is tinytiny compared to the atom as acompared to the atom as a
$hole.$hole.
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RutherfordRutherford
Rutherford reasonedRutherford reasoned
that all of an atom-sthat all of an atom-s
positi&ely char%edpositi&ely char%ed
particles $ereparticles $ere
containedcontainedin thein the
nucleus. The ne%ati&elynucleus. The ne%ati&ely
char%ed particles $erechar%ed particles $ere
scatteredscatteredoutside theoutside thenucleus around thenucleus around the
atom-satom-s ed%eed%e..
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!ohr Model!ohr Model
In 797B" the DanishIn 797B" the Danishscientist iels !ohrscientist iels !ohr
proposed anproposed an
impro&ement. In hisimpro&ement. In hismodel" he placedmodel" he placed
each electron in aeach electron in a
specificspecific
ener%yener%y
le&el.le&el.
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!ohr Model!ohr Model
Accordin% to !ohr-sAccordin% to !ohr-satomic model"atomic model"electrons mo&e inelectrons mo&e indefinitedefinite or#itsor#its
around the nucleus"around the nucleus"much lie planetsmuch lie planetscircle the sun. Thesecircle the sun. Theseor#its" or ener%yor#its" or ener%y
le&elsle&els" are located at" are located atcertaincertaindistancesdistancesfrom the nucleus.from the nucleus.
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Wave Model
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The +a&e ModelThe +a&e Model
Today-s atomicToday-s atomicmodel is #ased onmodel is #ased onthe principles ofthe principles of$a&e$a&emechanicsmechanics..
Accordin% to theAccordin% to thetheory of $aðeory of $a&emechanics" electronsmechanics" electronsdo not mo&edo not mo&ea#outa#out
an atom in aan atom in a definitedefinitepath"path"lie the planetslie the planetsaround the sun.around the sun.
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The +a&e ModelThe +a&e Model
In fact" it isIn fact" it is impossi#leimpossi#leto determine the e'actto determine the e'actlocation of an electron. Thelocation of an electron. The pro#a#lepro#a#lelocation of anlocation of anelectron is #ased on ho$ muchelectron is #ased on ho$ much ener%yener%ythe electronthe electronhas.has.
Accordin% to the modern atomic model" at atom hasAccordin% to the modern atomic model" at atom hasaa small positi&ely char%ed nucleussmallpositi&ely char%ed nucleussurrounded #y asurrounded #y alar%e re%ion in $hich there are enou%h electrons tolar%e re%ion in $hich there are enou%h electrons tomae an atom neutral.mae an atom neutral.
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Electron "lo#$%Electron "lo#$%
A space in $hichA space in $hichelectrons are liely to #eelectrons are liely to #efound.found.
ElectronsElectrons $hirl$hirla#out thea#out the
nucleus #illions of timesnucleus #illions of timesin one secondin one second
They are not mo&in%They are not mo&in%around inaround in randomrandompatterns.patterns.
ocation of electronsocation of electronsdepends upon ho$ muchdepends upon ho$ muchener%yener%ythe electron has.the electron has.
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Indi&isi#leIndi&isi#le ElectronElectron ucleusucleus Or#itOr#it ElectronElectron
CloudCloud
/ree/ree
DaltonDalton
ThomsonThomson
RutherfordRutherford
!ohr!ohr
+a&e+a&e