Atomic models Dr. vijender singh
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The atomic model has changed significantly over time based on new evidence and experiments. Early philosophers proposed that atoms were indivisible spheres, while later scientists like Thomson and Rutherford provided evidence that atoms have internal structure, including a small, dense nucleus surrounded by electrons. The current wave model depicts electrons as existing in probabilistic electron clouds rather than definite orbits, representing our most accurate understanding of atomic structure to date.
Atomic models Dr. vijender singh
- 1. Models of the AtomModels of the Atom a Historical Perspectivea Historical Perspective Dr. Vijender Singh GDC Memorial Degree College Bahal
- 2. Atomos: Not to Be CutAtomos: Not to Be Cut The History of Atomic TheoryThe History of Atomic Theory
- 3. Atomic ModelsAtomic Models This model of theThis model of the atom may lookatom may look familiar to you. This isfamiliar to you. This is the Bohr model. Inthe Bohr model. In this model, thethis model, the nucleus is orbited bynucleus is orbited by electrons, which areelectrons, which are in different energyin different energy levels.levels. A model uses familiar ideas toA model uses familiar ideas to explain unfamiliar factsexplain unfamiliar facts observed in nature.observed in nature. A model can be changed asA model can be changed as new information is collected.new information is collected.
- 4. The atomicThe atomic model hasmodel has changedchanged throughout thethroughout the centuries,centuries, starting in 400starting in 400 BC, when itBC, when it looked likelooked like aa billiard ballbilliard ball →→
- 5. Who are these men?Who are these men? In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.
- 6. DemocritusDemocritus This is the GreekThis is the Greek philosopher Democritusphilosopher Democritus who began the search forwho began the search for a description of mattera description of matter more thanmore than 24002400 yearsyears ago.ago. He asked: CouldHe asked: Could matter be divided intomatter be divided into smaller and smallersmaller and smaller pieces forever, or waspieces forever, or was there athere a limitlimit to theto the number of times anumber of times a piece of matter couldpiece of matter could bebe divideddivided?? 400 BC
- 7. AtomosAtomos His theory: Matter could notHis theory: Matter could not be divided into smaller andbe divided into smaller and smaller pieces forever,smaller pieces forever, eventually the smallesteventually the smallest possible piece would bepossible piece would be obtained.obtained. This piece would beThis piece would be indivisible.indivisible. He named the smallestHe named the smallest piece of matter “atomos,”piece of matter “atomos,” meaning “not to be cut.”meaning “not to be cut.”
- 8. AtomosAtomos To Democritus, atomsTo Democritus, atoms werewere smallsmall, hard, hard particles that were allparticles that were all made of the samemade of the same material but werematerial but were differentdifferent shapes andshapes and sizes.sizes. Atoms wereAtoms were infiniteinfinite inin number, alwaysnumber, always moving and capablemoving and capable of joining together.of joining together.
- 9. This theory was ignored andThis theory was ignored and forgotten for more thanforgotten for more than 20002000 years!years!
- 10. Why?Why? The eminentThe eminent philosophersphilosophers of the time,of the time, AristotleAristotle andand Plato, had aPlato, had a moremore respected,respected, (and ultimately(and ultimately wrongwrong) theory.) theory. Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.
- 12. Dalton’s ModelDalton’s Model In the early 1800s,In the early 1800s, the Englishthe English Chemist JohnChemist John DaltonDalton performed aperformed a number ofnumber of experiments thatexperiments that eventually led toeventually led to the acceptance ofthe acceptance of the idea of atoms.the idea of atoms.
- 13. Dalton’s TheoryDalton’s Theory He deduced that allHe deduced that all elementselements are composed ofare composed of atoms. Atoms areatoms. Atoms are indivisible andindivisible and indestructible particles.indestructible particles. Atoms of theAtoms of the samesame elementelement are exactly alike.are exactly alike. Atoms ofAtoms of differentdifferent elementselements areare differentdifferent.. CompoundsCompounds are formed byare formed by the joining of atoms of twothe joining of atoms of two or more elements.or more elements.
- 14. .. This theoryThis theory became onebecame one of theof the foundationsfoundations of modernof modern chemistry.chemistry.
- 15. Thomson’s Plum PuddingThomson’s Plum Pudding ModelModel InIn 18971897, the, the English scientistEnglish scientist J.J. ThomsonJ.J. Thomson provided the firstprovided the first hint that an atomhint that an atom is made of evenis made of even smallersmaller particles.particles.
- 16. Thomson’s “Plum Pudding” ModelThomson’s “Plum Pudding” Model Thomson suggested that the electrons in an atom were embedded in a positively charged, diffuse sphere. (Early 20th century) Claim: Atoms contain an equal amount of positive charge as negative charge
- 17. Thomson ModelThomson Model He proposed aHe proposed a model of the atommodel of the atom that is sometimesthat is sometimes called the “called the “PlumPlum PuddingPudding” model.” model. Atoms were madeAtoms were made from a positivelyfrom a positively chargedcharged substancesubstance with negativelywith negatively charged electronscharged electrons scatteredscattered about,about, like raisins in alike raisins in a pudding.pudding.
- 18. Thomson’s “Plum Pudding” ModelThomson’s “Plum Pudding” Model Reasoning:Reasoning: Since atoms were electrically neutral butSince atoms were electrically neutral but contained negatively charged electrons, theycontained negatively charged electrons, they must also contain an equal amount of positivemust also contain an equal amount of positive charge.charge. Thomson had no experimental evidence for hisThomson had no experimental evidence for his model but built on Lord Kelvin’s idea thatmodel but built on Lord Kelvin’s idea that positive charge in an atom was spread evenlypositive charge in an atom was spread evenly and diffusely throughout a spherical shape.and diffusely throughout a spherical shape. (Early 20th century)
- 19. Thomson ModelThomson Model Thomson studiedThomson studied thethe passagepassage of anof an electric currentelectric current through a gas.through a gas. As the currentAs the current passed throughpassed through the gas, it gave offthe gas, it gave off rays ofrays of negativelynegatively charged particles.charged particles.
- 20. Thomson ModelThomson Model This surprisedThis surprised Thomson,Thomson, because thebecause the atoms of the gasatoms of the gas were uncharged.were uncharged. Where had theWhere had the negative chargesnegative charges come from?come from? Where did they come from?
- 21. Thomson concluded that the negative charges came from within the atom. A particle smaller than an atom had to exist. The atom was divisible! Thomson called the negatively charged “corpuscles,” today known as electrons. Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. But he could never find them.
- 22. Rutherford’s Gold FoilRutherford’s Gold Foil ExperimentExperiment In 1908, theIn 1908, the English physicistEnglish physicist Ernest RutherfordErnest Rutherford was hard at workwas hard at work on an experimenton an experiment that seemed tothat seemed to have little to dohave little to do with unraveling thewith unraveling the mysteries of themysteries of the atomic structure.atomic structure.
- 23. Rutherford’s experiment InvolvedRutherford’s experiment Involved firing a stream of tinyfiring a stream of tiny positivelypositively chargedcharged particles at a thin sheet ofparticles at a thin sheet of gold foilgold foil (2000 atoms thick)(2000 atoms thick) Rutherford’s Gold FoilRutherford’s Gold Foil ExperimentExperiment
- 24. MostMost of the positivelyof the positively charged “bullets” passedcharged “bullets” passed right through the goldright through the gold atoms in the sheet ofatoms in the sheet of gold foilgold foil without changingwithout changing course at all.course at all. SomeSome of the positivelyof the positively charged “bullets,”charged “bullets,” however, did bouncehowever, did bounce away from the gold sheetaway from the gold sheet as if they had hitas if they had hit somethingsomething solidsolid. He. He knew that positiveknew that positive chargescharges repelrepel positivepositive charges.charges. Rutherford’s Gold FoilRutherford’s Gold Foil ExperimentExperiment
- 26. This could only mean that the gold atoms in theThis could only mean that the gold atoms in the sheet were mostlysheet were mostly open spaceopen space. Atoms were. Atoms were notnot a pudding filled with a positively chargeda pudding filled with a positively charged material.material. Rutherford concluded that an atom had aRutherford concluded that an atom had a small,small, dense, positively charged centerdense, positively charged center thatthat repelledrepelled his positively charged “bullets.”his positively charged “bullets.” He called the center of the atom the “He called the center of the atom the “nucleusnucleus”” The nucleus isThe nucleus is tinytiny compared to the atom as acompared to the atom as a whole.whole.
- 27. RutherfordRutherford Rutherford reasonedRutherford reasoned that all of an atom’sthat all of an atom’s positively chargedpositively charged particles wereparticles were containedcontained in thein the nucleus. Thenucleus. The negatively chargednegatively charged particles wereparticles were scatteredscattered outside theoutside the nucleus around thenucleus around the atom’satom’s edgeedge..
- 28. Bohr ModelBohr Model In 1913, theIn 1913, the Danish scientistDanish scientist Niels BohrNiels Bohr proposed anproposed an improvement. Inimprovement. In his model, hehis model, he placed eachplaced each electron in aelectron in a specificspecific energyenergy level.level.
- 29. Bohr ModelBohr Model According toAccording to Bohr’s atomicBohr’s atomic model, electronsmodel, electrons move in definitemove in definite orbitsorbits around thearound the nucleus, much likenucleus, much like planets circle theplanets circle the sun. These orbits,sun. These orbits, or energyor energy levelslevels,, are located atare located at certaincertain distancesdistances from the nucleus.from the nucleus.
- 30. This model of the atom isThis model of the atom is still the most famous ofstill the most famous of all models, and though itall models, and though it is not the most accurate,is not the most accurate, it predicts chemicalit predicts chemical reactions very well. (It isreactions very well. (It is important to remember,important to remember, though, that atomsthough, that atoms probably do not reallyprobably do not really look like this.)look like this.)
- 31. Wave Model
- 32. The Wave ModelThe Wave Model Today’s atomicToday’s atomic model is based onmodel is based on the principles ofthe principles of wavewave mechanicsmechanics.. According to theAccording to the theory of wavetheory of wave mechanics,mechanics, electronselectrons do notdo not movemove about anabout an atom in aatom in a definitedefinite path,path, like thelike the planets around theplanets around the sun.sun.
- 33. Wave Model of Atoms:Wave Model of Atoms:
- 34. The Wave ModelThe Wave Model In fact, it isIn fact, it is impossibleimpossible to determine the exactto determine the exact location of an electron. Thelocation of an electron. The probableprobable location oflocation of an electron is based on how muchan electron is based on how much energyenergy thethe electron has.electron has. According to the modern atomic model, at atomAccording to the modern atomic model, at atom has ahas a small positively charged nucleussmall positively charged nucleus surrounded by a large region in which there aresurrounded by a large region in which there are enough electrons to make an atom neutral.enough electrons to make an atom neutral.
- 35. Electron Cloud:Electron Cloud: A space in whichA space in which electrons are likely to beelectrons are likely to be found.found. ElectronsElectrons whirlwhirl about theabout the nucleus billions of timesnucleus billions of times in one secondin one second They are not movingThey are not moving around inaround in randomrandom patterns.patterns. Location of electronsLocation of electrons depends upon how muchdepends upon how much energyenergy the electron has.the electron has.
- 36. The Cloud ModelThe Cloud Model
- 37. The Wave Mechanical ModelThe Wave Mechanical Model AnAn orbitalorbital is described as ais described as a region in which an electron isregion in which an electron is most likely to be found.most likely to be found.
- 38. Electron Cloud:Electron Cloud: Depending on their energy they are locked into aDepending on their energy they are locked into a certain area in the cloud.certain area in the cloud. Electrons with theElectrons with the lowestlowest energy are found inenergy are found in the energy levelthe energy level closestclosest to the nucleusto the nucleus Electrons with theElectrons with the highesthighest energy are foundenergy are found in thein the outermostoutermost energy levels, farther fromenergy levels, farther from the nucleus.the nucleus.
- 39. IndivisibleIndivisible ElectronElectron NucleusNucleus OrbitOrbit ElectronElectron CloudCloud GreekGreek XX DaltonDalton XX ThomsonThomson XX RutherfordRutherford XX XX BohrBohr XX XX XX WaveWave XX XX XX
Editor's Notes
- #17: Atoms contain an equal amount of positive charge as negative charge (Because atoms have no overall charge but are known to contain negatively charged electrons)
- #37: Erwin Schrödinger built upon the thoughts of Bohr yet took them in a new direction. He developed the probability function for the Hydrogen atom (and a few others). The probability function basically describes a cloud-like region where the electron is likely to be found. It can not say with any certainty, where the electron actually is at any point in time, yet can describe where it ought to be. Clarity through fuzziness, is one way to describe the idea. The model based on this probability equation can best be described as the cloud model.