---Topic Dalton atomic Theory--- Class 9th students' pptx.

1. Topic- Dalton’s atomic theory

2. KEY POINT
• DALTON’SATOMICTHEORYPROPOSEDTHATALL MATTERWASCOMPOSED
OF ATOMS,INDIVISIBLEANDINDESTRUCTIBLEBUILDINGBLOCKS.WHILE
ALL ATOMSOF AN ELEMENTWEREIDENTICAL,DIFFERENTELEMENTSHAD
ATOMSOF DIFFERINGSIZE ANDMASS.
• DALTON’SATOMICTHEORYALSOSTATEDTHATALLCOMPOUNDSWERE
COMPOSEDOFCOMBINATIONSOF THESEATOMSIN DEFINEDRATIOS.
• DALTONALSOPOSTULATEDTHATCHEMICALREACTIONSRESULTEDIN
THEREARRANGEMENTOF THEREACTINGATOMS.

3. TERMS
• ATOMTHESMALLESTPOSSIBLEAMOUNTOF MATTERTHATSTILLRETAINS
ITSIDENTITYASA CHEMICALELEMENT,NOWKNOWNTOCONSISTOFA
NUCLEUSSURROUNDEDBYELECTRONS.
• ATOMICMASSUNITTHESTANDARDUNITTHATIS USEDFORINDICATING
MASSOFANATOM.

4. HISTORY OF DALTON’S
ATOMIC THEORY
ALTHOUGHTHECONCEPTOFTHEATOMDATESBACKTOTHEIDEASOFDEMOCRITUS,THEENGLISH
METEOROLOGISTANDCHEMISTJOHNDALTONFORMULATEDTHEFIRSTMODERNDESCRIPTIONOF
ITASTHEFUNDAMENTALBUILDINGBLOCKOFCHEMICALSTRUCTURES.DALTONDEVELOPEDTHE
LAWOFMULTIPLEPROPORTIONS(FIRSTPRESENTEDIN1803)BYSTUDYINGANDEXPANDINGUPON
THEWORKSOFANTOINELAVOISIERANDJOSEPHPROUST.
PROUSTHADSTUDIEDTINOXIDESANDFOUNDTHATTHEIRMASSESWEREEITHER88.1%TINAND
11.9%OXYGENOR78.7%TINAND21.3%OXYGEN(THESEWERETIN(II)OXIDEANDTINDIOXIDE
RESPECTIVELY).DALTONNOTEDFROMTHESEPERCENTAGESTHAT100GOFTINWILLCOMBINE
EITHERWITH13.5GOR27GOFOXYGEN;13.5AND27FORMARATIOOF1:2.DALTONFOUNDANATOMIC
THEORYOFMATTERCOULDELEGANTLYEXPLAINTHISCOMMONPATTERNINCHEMISTRY– INTHE
CASEOFPROUST’STINOXIDES,ONETINATOMWILLCOMBINEWITHEITHERONEORTWOOXYGEN
ATOMS.

5. Dalton also believedatomic theory couldexplainwhywaterabsorbed different gasesin different
proportions: for example, he found that water absorbed carbondioxide far better than it absorbed
nitrogen. Daltonhypothesizedthis was due to the differences in the mass and complexityof the gases’
respective particles. Indeed, carbondioxide molecules (CO2) are heavier and larger thannitrogen
molecules (N2).
Dalton proposed that each chemical element is composed of atoms of a single, unique type, and though
theycannot be alteredor destroyed by chemical means, theycan combineto form more complex
structures (chemical compounds). Since Dalton reachedhis conclusionsby experimentation and
examination of the results in an empirical fashion, this marked the first trulyscientific theoryof the
atom.

6. DALTON’S ATOMIC
THEORY
THEMAINPOSTULATESOFDALTON’SATOMICTHEORY WERE:
• EVERYTHINGIS COMPOSEDOF ATOMS,WHICHARETHEINDIVISIBLEBUILDINGBLOCKSOF
MATTERANDCANNOTBE DESTROYED.
• ALLATOMSOF AN ELEMENTAREIDENTICAL.
• THEATOMSOF DIFFERENTELEMENTSVARYIN SIZEANDMASS.
• COMPOUNDSAREPRODUCEDTHROUGHDIFFERENTWHOLE-NUMBERCOMBINATIONSOF
ATOMS.
• A CHEMICALREACTIONRESULTSIN THEREARRANGEMENTOFATOMSIN THEREACTANTAND
PRODUCTCOMPOUNDS.
ATOMICTHEORYHASBEENREVISEDOVERTHEYEARSTOINCORPORATETHEEXISTENCEOFATOMIC
ISOTOPESANDTHEINTERCONVERSIONOFMASSANDENERGY.IN ADDITION,THEDISCOVERYOF
SUBATOMICPARTICLESHASSHOWNTHATATOMSCANBE DIVIDEDINTOSMALLERPARTS.HOWEVER,
DALTON’SIMPORTANCEIN THEDEVELOPMENTOF MODERNATOMICTHEORYHASBEEN
RECOGNIZEDBY THEDESIGNATIONOF THEATOMICMASSUNITAS A DALTON