2. The AtomThe AtomFrom the Greek prefix A- meaning“not”And the Greek Root –tomos meaning“cut””Together meaning “uncuttable”The ancient Greeks wanted to learn aboutthe smallest particle of matter
4. Ancient Greek Model ofAtomsThe ancient Greeks were one of theearliest cultures to investigate the conceptof the atom.Democtitus and Aristotle , two Greekphilosophers came up with two alternatetheories
5. Democritus’ “Atom” DemocritusDemocritus believed that all matterconsisted of extremely small particles thatcould not be divided.He called these particles atoms (from theGreek “ατοµος”, meaning “uncut” or“indivisible”).
6. Democritus’ “Atom”He believed there were different types ofatoms with specific sets of properties. Theatoms in liquids, for example, were roundand smooth, but the atoms in solids wererough and prickly
8. Aristotle’s “Atom”Aristotle did not think there was a limit tothe number of times matter could bedivided. He thought that all substances were builtup from only four elements—earth, air,fire, and water. These elements were acombination of four qualities—hot, cold,dry, and wet.
9. Aristotle’s “Atom”Fire was a combination of hot and dry.Water was a combination of cold and wet.
11. Dalton’s Model of the AtomDalton proposed the theory that all matteris made up of individual particles, calledatoms, which cannot be divided.All atoms of the same element have thesame mass, and atoms of differentelements have different masses.
12. Dalton’s Model of the AtomCompounds contain atoms of more thanone element.He developed a theory to explain why theelements in a compound always join in thesame wayIn a particular compound, atoms ofdifferent elements always combine in thesame way
13. The Dalton ModelThe Dalton Model
14. J. J. ThomsonJ. J. Thomson
15. J. J. Thomson’s Model of theJ. J. Thomson’s Model of theAtomAtomIn Thomson’s experiments with beams ofcharged particles in a sealed glass tubeled him to the conclusion that atoms weremade of even smaller particlesThomson reasoned that if the charge of anatom is neutral, the atom must containparticles with both positive and negativecharges in equal amounts.
16. J. J. Thomson’s Model of theJ. J. Thomson’s Model of theAtomAtomIn Thomson’s experiments with beams ofcharged particles in a sealed glass tubeled him to the conclusion that atoms weremade of even smaller particlesThomson reasoned that if the charge of anatom is neutral, the atom must containparticles with both positive and negativecharges in equal amounts.
17. The Thomson ModelThe Thomson ModelIn Thomson’s modelof the atom, thenegative chargeswere evenly scatteredthroughout an atomfilled with a positivelycharged mass ofmatter. The model iscalled the “plumpudding” model.
19. Rutherford’s Model of theRutherford’s Model of theAtomAtomTo account for these results, Rutherfordhypothesized that the positive charge ofan atom must be concentrated in a verysmall area that he called the nucleus.Further experiments with other elementsled him to conclude that the positivecharge of an atom is determined by thenumber of protons in the nucleus.Each proton has a charge of +1.
20. Rutherford’s Model of the AtomRutherford’s Model of the Atomand Gold Foil Testand Gold Foil Test
21. Niels BohrNiels Bohr
22. The Bohr Model of the AtomThe Bohr Model of the AtomIn Bohr’s model, electrons move withconstant speed in fixed orbits aroundthe nucleus, like planets around asun.Electrons gain or lose energy whenthey move between orbits or energylevels. Energy levels are like stairs ona staircase or shelves in a bookshelf
23. The Bohr Model of the AtomThe Bohr Model of the AtomEvidence for discrete, unique energylevels comes from the light given offwhen energy is added to the atoms ofan element (such as when fireworksexplode or electricity is added to aneon light). No two elements have thesame set of energy levels, so theemission pattern can be used toidentify the element.
24. The Bohr ModelThe Bohr Model
25. ChadwickChadwickDeduced the existence of neutronsfrom experiments in which a chargedobject did not deflect the path ofparticles he produced.
27. Schrodinger & Heisenberg’sSchrodinger & Heisenberg’sElectron Cloud ModelElectron Cloud ModelAn electron in an atom can moveAn electron in an atom can movefrom one energy level to anotherfrom one energy level to anotherwhen the atom gains or loseswhen the atom gains or losesenergyenergy.
28. Scientists discovered that electronsare less predictable than in Bohr’smodel of fixed orbits. They use anelectron cloud model to show themost likely locations for electronsas they move around the nucleus.
29. The electron cloud represents allthe orbitals in an atom. An orbital isa region of space around thenucleus where an electron is likelyto be found. Orbitals come indifferent sizes, shapes, andlocations
30. An electron configuration is thearrangement of electrons in theorbitals of an atom. The most stableelectron configuration is the one inwhich the electrons are in orbitalswith the lowest possible energies
31. The Electron Cloud ModelThe Electron Cloud Model
32. The Nature of Science Each scientist wascorrect for his timeand ability to makeobservations. As improvements intechnology cameabout, each laterscientist proved theprevious scientist(s)slightly incorrect. Now there is a totallydifferent model of theatom from the firstmodel presented byThompson. Only some of thetheories of eachscientist remain. In general…
33. The Nature of ScienceThe Nature of Science As the ability toAs the ability tomake bettermake betterobservationsobservationsimproves, theimproves, theknowledge mayknowledge mayprove or disproveprove or disprovewhat we have heldwhat we have heldto be true into be true inscience.science.