Discovery of Subatomic Particles of an Atom

The discovery of subatomic particles of an Atom. Its Nuceus and the model of an Atom

1. 1
DISCOVERY OF
SUBATOMIIC PARTICLES
&
ATOMIC MODEL

2. 2
INTRODUCTION
TheAtomisabasicunitofmatterthatconsistsofa
dense,centralnucleussurroundedbyacloudof
negativelychargedelectrons.
TheIndianswerethefirsttomakeanattempttowardsthe
discoveryofatomintheearly6
th
centuryBCE.The
BhagvadGitamentions‘anu’or“anor”whichissanskrit
for‘atom’.Butthemainphilosophyofmostofthe
philosopherssuchasDharmakritiwasthatmatteris
madeupof4elements-fire,earth,waterandair.
Inthe5
th
CenturyBC,LeucippusandDemocritus
proposedthatallmatterwascomposedofsmallinvisible
particlescalled“atoms”.
Foralongtime,itwasbelievedthatatomsarethe
ultimateparticlesthatmatterismadeupofandthatthese
atomscannotbedividedfurther.Theexperiments
conductedduringthelatterhalfofthenineteenthcentury
andearlyyearsofthetwentiethcenturyrevealedthatthe
atomisnottheultimateparticle.Thecontinuedeffortsof
thescientistsledtothediscoveryofsubatomic
particles.
Democritus Leucippus
Democritus Leucippus

3. 3
Discovery of Subatomic Particles
Theadvancesinatomicstructureandquantummechanicshave
ledtothediscoveryofotherfundamentalparticles.Thediscovery
ofsubatomicparticleshasbeenthebaseformanyother
discoveriesandinventions.
Theatomicstructureofanelementreferstotheconstitutionofits
nucleusandthearrangementoftheelectronsaroundit.Primarily,
theatomicstructureofmatterismadeupofprotons,electronsand
neutrons.
Theprotonsandneutronsmakeupthenucleusoftheatom,
whichissurroundedbytheelectronsbelongingtotheatom.
Theatomicnumberofanelementdescribesthetotalnumberof
protonsinitsnucleus.
Neutralatomshaveequalnumbersofprotonsandelectrons.
However,atomsmaygainorloseelectronsinordertoincrease
theirstabilityandtheresultingchargedentityiscalledanion.
Atomsofdifferentelementshavedifferentatomicstructures
becausetheycontaindifferentnumbersofprotonsandelectrons.
Thisisthereasonfortheuniquecharacteristicsofdifferent
elements.

4. 4
Atomic Model
Inthe18thand19thcenturies,manyscientistsattemptedto
explainthestructureoftheatomwiththehelpofatomicmodels.
Eachofthesemodelshadtheirownmeritsanddemeritsandwere
pivotaltothedevelopmentofthemodernatomicmodel.The
mostnotablecontributionstothefieldwerebythescientistsJohn
Dalton,J.J.Thomson,ErnestRutherford,NielsBohr&James
Chadwick.
Dalton’sAtomicTheory:
The idea of atomic theory was revived by John Dalton (1766-1844)
2,000 years after Democritus first proposed about it.
In1800,JohnDaltonperformedaseriesofexperimentsshowing
thematterconsistsoflumpyparticlescalled“atoms”.
His Findings led to the formulation of what is commonly known as
“Dalton’s Atomic Theory”.
DaltonformulatedhistheorybasedonAntoineLavoiser’s(1743-
1794)lawofconservationofmassandJosephProust’s(1754-
1826)lawofdefiniteproportion.
AccordingtothepostulatesproposedbyDalton,theatomic
structurecomprisedatoms,thesmallestparticleresponsiblefor
thechemicalreactionstooccur.
John Dalton

5. 5
Dalton’s Atomic Model & Postulates
TheEnglishchemistJohnDaltonsuggestedthatallmatteris
madeupofatoms,whichwereindivisibleandindestructible.He
alsostatedthatalltheatomsofanelementwereexactlythe
same,buttheatomsofdifferentelementsdifferinsizeandmass.
The following are the postulates of his theory:
Every matter is made up of atoms.
Atoms are indivisible.
Specific elements have only one type of atoms in them.
Each atom has its own constant mass that varies from element to
element.
Atoms undergo rearrangement during a chemical reaction.
Atoms can neither be created nor be destroyed but can be
transformed from one form to another.
Dalton’satomictheorysuccessfullyexplainedtheLawsof
chemicalreactions,namely,theLawofconservationofmass,Law
ofconstantproperties,LawofmultipleproportionsandLawof
reciprocalproportions.
However,duringhistime,(1800s),somescientistsstilldidnot
believethattherewasanindivisibleatomfoundinallMatter.

6. 6
Thomson Atomic Model
TheEnglishchemistSirJosephJohnThomsonputforthhis
modeldescribingtheatomicstructureintheearly1900s.
HewaslaterawardedtheNobelprizeforthediscoveryof
“electrons”.Hisworkisbasedonanexperimentcalledcathode
rayexperiment.Theconstructionofworkingoftheexperimentis
asfollows:
Conclusions:
Basedonconclusionsfromhiscathoderayexperiment,Thomson
describedtheatomicstructureasapositivelychargedsphereinto
whichnegativelychargedelectronswereembedded.
Itiscommonlyreferredtoasthe“plumpuddingmodel”because
itcanbevisualizedasaplumpuddingdishwherethepudding
describesthepositivelychargedatomandtheplumpieces
describetheelectrons.
Thomson’satomicstructuredescribedatomsaselectrically
neutral,i.e.thepositiveandthenegativechargeswereofequal
magnitude.
LimitationsofThomson’sAtomicStructure:Thomson’satomic
modeldoesnotclearlyexplainthestabilityofanatom.
Withallthisevidence,Thompsonconcludedthatcathoderaysare
madeofnegativelychargedparticlescalled“electrons”.
J.J.THOMSON

7. 7
Rutherford Atomic Model
Rutherford,astudentofJ.J.Thomsonmodifiedtheatomic
structurewiththediscoveryofanothersubatomicparticlecalled
“Nucleus”.Hisatomicmodelisbasedonthe“Alpharay
scatteringexperiment.”
ItwasErnestRutherford(1871-1937)whocoinedtheterm
“proton”forthepositivelychargedparticleinanatom
Rutherford’sStructureofAtom:
Basedontheexperimentandconclusions,Rutherfordproposed
hisownatomicstructurewhichisasfollows.
Thenucleusisatthecenterofanatom,wheremostofthecharge
andmassareconcentrated.
Atomicstructureisspherical.
Electronsrevolvearoundthenucleusinacircularorbit,similarto
thewayplanetsorbitthesun.
The electrons move around the nucleus, the protons found inside
the nucleus are positively charged.
The number of protons is equal to the number of electrons.
Later he postulated the existence of a neutral particle in the
nucleus to make up for, he calculated mass efficiency in the atom
studied.
Rutherford

8. 8
NielsBohr & James Chadwick Model
NielsBohr’sPlanetaryModel
The electrons move around the nucleus in fixed orbit & electron in
a particular orbit has constant energy.
An electron can absorb energy and move to a higher energy orbit
of larger radius.
Anexcitedelectroncanfallbacktoitsoriginalorbitbyemitting
energyasradiation.
JamesChadwick’sModel
The“Neutron”wasdiscoveredbyJamesChadwickintheyear
1932.
Jamesatomicmodelisknownasthequantummechanical
modeloftheatom.In1932,JamesChadwickbombarded
berylliumatomswithalphaparticles.Anunknownradiationwas
produced.Chadwickinterpretedthisradiationasbeingcomposed
ofparticleswithaneutralelectricalchargeandtheapproximate
massofaproton.
Accordingtohim,thenucleusofanatomcontains
“Neutrons”,electricallyneutralparticleswithamasssimilartothat
ofproton.
Thecontinuedeffortsofthescientistsledtothediscoveryof
subatomicparticles.Thethreeprimarysubatomicparticlesthat
constituteanatomareElectron,Proton&Neutron.
NielsBohr
J.Chadwick

9. 9
Electron, Proton & Neutron
Electrons
ProtonsProton:
Protonsarepositivelychargedsubatomicparticles.Thechargeof
aprotonis1e,whichcorrespondstoapproximately1.602×10-19.
Themassofaprotonisapproximately1.672×10-24
Protonsareover1800timesheavierthanelectrons.
Thetotalnumberofprotonsintheatomsofanelementisalways
equaltotheatomicnumberoftheelement
ThediscoveryofprotonsiscreditedtoErnestRutherford.
Neutron:
Themassofaneutronisalmostthesameasthatofaprotoni.e.
1.674×10-24.
Neutronsareelectricallyneutralparticlesandcarrynocharge.
Differentisotopesofanelementhavethesamenumberofprotons
butvaryinthenumberofneutronspresentintheirrespective
nuclei.
TheneutronwasdiscoveredbyJamesChadwick.
Electron:
Thechargeofanelectronis-1e,whichapproximatesto-1.602×
10-19.
Themassofanelectronisapproximately9.1×10-31.
Duetotherelativelynegligiblemassofelectrons,theyareignored
whencalculatingthemassofanatom.
J.J.Thompsoniscreditedwiththediscoveryofelectrons
Proton
Electrons

10. 10
Nucleus of an Atom
Electrons
Nucleus:
Anatomnucleusismadeupofprotonsandneutrons.Protons
bearapositivechargeequaltotheelectronsorbitingaround,and
theneutronsbearnochargebutweighthesameastheprotons.
Theatomnucleuscreatestheforcerequiredtokeepthe
atomtogetherandinorder.
Anucleusisidentifiedasintheexamplebelowbyitsatomic
numberZ(i.e.,thenumberofprotons),theneutronnumber,N,
andthemassnumber,A,whereA=Z+N.Theconventionfor
designatingnucleiisbyatomicnumber,Z,andmassnumber,A,
aswellasitschemicalsymbol.
Summary:
Thenucleusisasmall,denseregionatthecenteroftheatom.
Consistingofpositiveprotonsandneutralneutrons,thenucleus
hasanoverallpositivecharge.
Thenucleuscontainsvirtuallyalloftheatom'smass.
Strongnuclearforceholdstogetherprotonsandneutronsinthe
nucleus,andovercomestheelectricforceofrepulsionbetween
protons.

11. 11
Thank You
Bibliography :
1)https://www.britannica.com/science/atomic-model
2)https://en.wikipedia.org/wiki/Rutherford_model
3)https://www2.lbl.gov/abc/wallchart/chapters/02/2.html-Nucleus
4)https://www.livescience.com/37206-atom-definition.html
5)https://edu.glogster.com/glog/james-chadwick/23jfieeaktw?=glogpedia-source
6)https://byjus.com/chemistry/rutherfords-model-of-atoms-and-its-limitations/
7)https://byjus.com/jee/atomic-structure/
Acknowledgement:
IwishtoexpressmydeepgratitudeandsincerethankstothePrincipal,MrsSudhaMenon,
NorthPointSchoolforherencouragementandfacilitiesthatsheprovidedforthisprojectwork.
IextendmyheartythankstoMrs.AditiNebChemistryteacher,whoguidedmetothe
successfulcompletionofthisproject.Itakethisopportunitytoexpressmydeepsenseof
gratitudeforherinvaluableguidance,constantencouragement,immensemotivation,which
hassustainedmyeffortsatallthestagesofthisProjectwork…
Ican’tforgettooffermysincerethankstoparentsandalsotomysisterwhohelpedmeto
carryoutthisprojectworksuccessfulandfortheirvaluableadviceandsupport,whichI
receivedfromthemtimetotime….