atomic theory(1) 2

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Atomic Theory Atomic Theory



400B.C.400B.C.

Early Greek philosophers pondered the fundamental nature of matter:Early Greek philosophers pondered the fundamental nature of matter:

Is it continuous and infinitelyIs it continuous and infinitelydivisible?divisible?

!ristotle"!ristotle"

Is it divisible only until a basic#Is it divisible only until a basic#indivisible particle that cannot beindivisible particle that cannot bedivided any further is reached?divided any further is reached?

$emocritus"$emocritus"



$emocritus is the first to use the term$emocritus is the first to use the term%atom&%atom& from the Greek 'ordfrom the Greek 'ord atomosatomos

meanin(meanin( indivisible.indivisible.

$emocritus 'as not believed$emocritus 'as not believedand it 'ould be thousands of and it 'ould be thousands of

years before scientists 'ouldyears before scientists 'ould

re)visit this idea.re)visit this idea.

*e believed the 'orld 'as made of:*e believed the 'orld 'as made of:

+." atoms+." atoms,." empty space,." empty space



-hat happened in the net ,000-hat happened in the net ,000

years?years?

/he !tomic /heory is published/he !tomic /heory is published

in +01.in +01.



2ore than ,000 years after $emocritus# an2ore than ,000 years after $emocritus# anEn(lish scientist and school teacher#En(lish scientist and school teacher# 3ohn3ohn$alton$alton# proposed an# proposed an !tomic /heory!tomic /heory of hisof hiso'n and published a series of papers in theo'n and published a series of papers in theearly +00s.early +00s.

Because of this#Because of this# John Dalton is known as:John Dalton is known as:

The Father of the Atomic Theory.The Father of the Atomic Theor

y.

John Dalton 1766-1844John Dalton 1766-1844



/he a's that 5hape the !tom/he a's that 5hape the !tom

/he a' of $efinite/he a' of $efinite 6roportions6roportions

! chemical compound al'ays contains the same! chemical compound al'ays contains the sameelements in eactly the same proportions by mass.elements in eactly the same proportions by mass.

H2O:

11% hydrogen

89% ox en



/he a' of Conservation of 2ass/he a' of Conservation of 2ass

2ass cannot be created or destroyed in ordinary2ass cannot be created or destroyed in ordinary

chemical or physical chan(es.chemical or physical chan(es.

Ca(NO3)2 + 2NaCl → CaCl2 + 2NaNO3



/he a' of 2ultiple 6roportions/he a' of 2ultiple 6roportions

If t'o elements form more than oneIf t'o elements form more than onecompound bet'een them e. C7 and C7compound bet'een them e. C7 and C7,,"#"#

then# the ratios of the masses of the secondthen# the ratios of the masses of the second

element 'hich combine 'ith a fied mass ofelement 'hich combine 'ith a fied mass ofthe first element 'ill be ratios of small 'holethe first element 'ill be ratios of small 'holenumbers.numbers.

Eamples:Eamples: C7 C7 C7 C7,,

+.00 ( C# +.11 ( 7"+.00 ( C# +.11 ( 7" +.00 ( C#+.00 ( C#

,.88 ( 7",.88 ( 7"

+:,"+:,"



3ohn $alton3ohn $alton9s !tomic /heory9s !tomic /heor y states thatstates that

!ll 2atter is made of atoms.!ll 2atter is made of atoms.

!toms of the same element are identical#and atoms!toms of the same element are identical#and atomsof different elements are different.of different elements are different.

!toms of different elements combine in simple!toms of different elements combine in simple'hole number ratios to form compounds.'hole number ratios to form compounds.

In chemical reactions# atoms are combined#In chemical reactions# atoms are combined#separated or rearran(ed.separated or rearran(ed.

!toms cannot be subdivided# created or destroyed.!toms cannot be subdivided# created or destroyed.



Atoms of Carbon: Atoms of Hydrogen:

!ll matter is composed of etremely small particles!ll matter is composed of etremely small particlescalled atoms.called atoms.

!ll atoms of a (iven element are identical# and are!ll atoms of a (iven element are identical# and aredifferent from those atoms of any other element.different from those atoms of any other element.

!toms cannot be subdivided# created# or destroyed.!toms cannot be subdivided# created# or destroyed.



Atoms of hydrogen and carbon canAtoms of hydrogen and carbon can

combine to form new substancescombine to form new substancescalled compounds…called compounds…

METHANE

CHCH44 1C : 4H1C : 4H

PROPANE

CC33HH88 3C : 8H3C : 8H

!toms of different elements combine in simple!toms of different elements combine in simple'hole)number ratios to form compounds.'hole)number ratios to form compounds.

a' of $efinite 6roportions ; a' of 2ultiple 6roportions"a' of $efinite 6roportions ; a' of 2ultiple 6roportions"



In chemical reactions# atoms are combined#In chemical reactions# atoms are combined#separated# or rearran(ed.separated# or rearran(ed.

a' of Conservation of 2ass"a' of Conservation of 2ass"

Synthesis of Methane:

++

1C 2H21CH4

++



$alton$alton9s theory 'as accepted by the scientific9s theory 'as accepted by the scientificcommunity# but over time parts of his theory arecommunity# but over time parts of his theory are<uestioned.<uestioned.

-here does $alton-here does $alton9s /heory break do'n?9s /heory break do'n?

!toms cannot be subdivided#created or!toms cannot be subdivided#created ordestroyed.destroyed.

)=o' 'e kno' of p)=o' 'e kno' of p>># n# noo# e# e))..

!toms of the same element are identical.!toms of the same element are identical.)=o' 'e kno' of)=o' 'e kno' of

isotopes.isotopes.



$alton$alton9s 6icture of the !tom9s 6icture of the !tom



Since Dalton! ti"e# "any "ore di!co$erie!

ao&t the ato" ha$e een "ade a! the re!&lt o'the dedicated endea$or! o' !cienti!t! ho

"ade ato"ic re!earch their li'e! or*



!n En(lish scientist#!n En(lish scientist# 5ir -illiam5ir -illiam

CrookesCrookes discovered the electron.discovered the electron.

William Crookes 1832-1919William Crookes 1832-1919



Cathode ay /ubeCathode ay /ube



In the late 1800s, the EnglishIn the late 1800s, the English

hysicist,hysicist, J. J. ThomsonJ. J. Thomson,,

determined a very lar(e char(e todetermined a very lar(e char(e tomass ratio of anmass ratio of an electronelectron..

Sir J. J. Thomson 1856-1940Sir J. J. Thomson 1856-1940



In the early +@00s# an !merican 6hysicist#In the early +@00s# an !merican 6hysicist# obertobert2illikan2illikan# determined the electron# determined the electron9s actual char(e9s actual char(e

usin( his famous oil)drop eperiment.usin( his famous oil)drop eperiment.

Robert Millikan 1868-1953



Eventually#Eventually# 3.3. /homson3.3. /homson proposed a ne'proposed a ne'atomic model# theatomic model# the 6A2)6A$$I=G 27$E6A2)6A$$I=G 27$E# in# in'hich electrons are evenly distributed'hich electrons are evenly distributed

throu(hout a sphere of positive char(e inthrou(hout a sphere of positive char(e insuch a 'ay that the atom is electricallysuch a 'ay that the atom is electricallyneutral.neutral.



!nother physicist#!nother physicist# Ernest utherfordErnest utherford##'ho 'as a student of /homson'ho 'as a student of /homson9s#9s#

disputed the 6lum 6uddin( model.disputed the 6lum 6uddin( model.

rnest R!ther"or# 1871-1937rnest R!ther"or# 1871-1937

!l i h l +@00 d i hi f!l i th l +@00 d i hi f ld f il

ld f il



!lso in the early +@00s# durin( his famous!lso in the early +@00s# durin( his famous (old foil(old foileperimenteperiment## Ernest utherfordErnest utherford bombarded a sheetbombarded a sheetof (old foil 'ith a beam of positively char(edof (old foil 'ith a beam of positively char(ed

particles called alpha particles.particles called alpha particles.

48

&ther'ord! al,ha ,article !cattering ex,eri"ent*

5.5

5ource of alpha particles ) 6olonium"5ource of alpha particles ) 6olonium"

G C



Gold oil Eperiment Conclusions:Gold oil Eperiment Conclusions:1*) -o!t o' the ato" i! e",ty !,ace*

2*) N&cle&! . !"all# den!e and ,o!iti$ely charged*



utherfordutherford9s 2odel of the !tom9s 2odel of the !tom

/h i i l h d



/he positively char(ed proton 'as/he positively char(ed proton 'asdiscovered by German physicistdiscovered by German physicist

Eu(in GoldsteinEu(in Goldstein..

!$in %ol#stein 1850-1930!$in %ol#stein 1850-1930

/h t t ll



/he neutron 'as eventually/he neutron 'as eventuallydiscovered by the En(lish 6hysicist#discovered by the En(lish 6hysicist#

5ir 3ames Chad'ick.5ir 3ames Chad'ick.

James &ha#'i(k 1891-1974

7 th l t t d t7 th l t t d t



7nce the electron# proton# and neutron7nce the electron# proton# and neutronhad been discovered# scientists be(an tohad been discovered# scientists be(an to

theorie about the arran(ement of thesetheorie about the arran(ement of theseparticles 'ithin the atom.particles 'ithin the atom.

=i l B h=i l B h $ i h h i i t$ i h h i i t



=iels Bohr =iels Bohr # a $anish physicist## a $anish physicist#developed thedeveloped the Bohr 2odelBohr 2odel of the atom.of the atom.

)iels *ohr 1885-196+)iels *ohr 1885-196+

! h! h " li $ th t th l t" li $ th t th l t



!ohr !ohr "elie#e$ that the electrons were"elie#e$ that the electrons were

locate$ in $istinct areas o%tsi$e of thelocate$ in $istinct areas o%tsi$e of the

n%cle%s which he calle$ energy le#els.n%cle%s which he calle$ energy le#els.

Energy level



&ince the atomic "om" research of '' II,&ince the atomic "om" research of '' II,m%ch more has "een $isco#ere$ a"o%t them%ch more has "een $isco#ere$ a"o%t the

atom that was first en#isione$ "yatom that was first en#isione$ "y

Democrit%s o#er ()00 years ago*Democrit%s o#er ()00 years ago*

2 d $ !t i 2 d l2 d $ !t i 2 d l



2odern $ay !tomic 2odel:2odern $ay !tomic 2odel:Er'in 5chr Er'in 5chr DDdin(er din(er

uantum 2echanical 2odel"uantum 2echanical 2odel"



In more recent years, +%arks ha#e "een slitIn more recent years, +%arks ha#e "een slit

into e#en smaller s%"atomic articles.into e#en smaller s%"atomic articles.

-#er the ast few $eca$es, hysicists ha#e-#er the ast few $eca$es, hysicists ha#e

$isco#ere$ new articles which they ha#e$isco#ere$ new articles which they ha#e

calle$calle$ +%arks+%arks/. These +%arks ha#e "een/. These +%arks ha#e "eenfo%n$ to "e the f%n$amental "%il$ing "locksfo%n$ to "e the f%n$amental "%il$ing "locks

of rotons an$ ne%trons.of rotons an$ ne%trons.



!f ! ha"e seen f#rther$it is by!f ! ha"e seen f#rther$it is by

standing #%on the sho#&ders ofstanding #%on the sho#&ders of

giants'(giants'(

)Sir !saa* Ne+ton)Sir !saa* Ne+ton

atomic theory(1) 2

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