6 DEVELOPS THE IDEA OF THE ATOM. 460 BC DemocritusDEVELOPS THE IDEA OF THE ATOM.He pounds materials in his mortar and pestle until he reduces them to smaller and smaller particles which he ultimately calls…ATOMOS(greek for indivisible)
7 Democritus’s Ideas Atoms are solid & homogeneous all atoms made of the same material.Different types of atoms have different shapes and sizes.The different shapes and sizes of the atoms determine the different properties of the substancesAtoms are infinite in number.
8 Earth, Fire, Air and Water approach to the nature of matter. AristotleEarth, Fire, Air and Water approach to the nature of matter.All substances made of these four elementsBlend these in different proportions to get all substancesTransmute Lead into GOLD
9 ARISTOTLE WINS!!!Democritus’ idea of “atoms” was ignored and forgotten for more than 2000 years!
10 Dalton combines the idea of elements with that of atoms! HISTORY OF THE ATOMJohn Dalton (England)1808All matter is made up of tiny spheres called …ATOMSDalton combines the idea of elements with that of atoms!
11 Dalton’s Atomic Theory Billiard Ball Model All elements are composed of atoms.indivisible and indestructibleAtoms of the same element are alikeAtoms of different elements are differentChemical reactions involve the rearrangement of atoms.
12 Evidence #1 It is possible to remove a negatively charged particle from an atom using electrical forces (Thomson 1897)Evidence #2: If a tiny particle is shot into the middle of an atom, it hits something dense in the center and bounces back in the direction from which it came. If a tiny particle is shot into the edges of the atom, it goes through. Most tiny particles shot at an atom will go through. (Rutherford, 1911)Evidence #3: The farther from the center of an atom the negatively charged particles are, the easier they are to remove (Bohr, 1913)Using the 5 models of the atom, answer discussion questions
19 PLUM PUDDING MODEL Atoms are now considered divisible 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's chargelike plums surrounded by pudding.Atoms are now considered divisible
21 HISTORY OF THE ATOM Ernest Rutherford 1910 Believed the plum pudding model of the atom was correct.Wanted to see how positively charged alpha particles (radioactive) interacted with solid matter.Shot them at gold foil which was only a few atoms thick.
22 Rutherford’s experiment Here’s what it looked like
32 Density and the AtomSince most of the particles went through, the atom was mostly emptyBecause the alpha particles deflected so much, the positive pieces in the core of the atom had to be very heavyPositive core had a small volume, big mass, big densityThis small dense positive area is the nucleus
33 HISTORY OF THE ATOM Niels Bohr 1913 Studied under Rutherford. Bohr refined Rutherford's ideaelectrons were in orbits (like planets orbiting the sun)each orbit could contain only a set number of electrons.
35 Bohr Model of Atom e- e- e- Increasing energyof orbitsn = 3e-n = 2n = 1e-e-A photon is emittedwith energy E = hfThe Bohr model of the atom, like many ideas inthe history of science, was at first prompted byand later partially disproved by experimentation.
36 The Electron Cloud Model Developed between the 1920’s and 1930’s by Werner Heisenberg and Erwin SchrodingerStates that the atom is mostly empty spaceTwo regionsNucleus- protons and neutronsElectron cloud- region where you have a high probability of finging an electron
37 Models of the Atom Dalton’s model (1803) Greek model (400 B.C.) Thomson’s plum-puddingmodel (1897)Rutherford’s model(1909)Bohr’s model(1913)Charge-cloud model(present)“Models of the Atom”Description: This slide shows he evolution of the concept of the atom from John Dalton to the present.Basic Concepts· The model of the atom changed over time as more and more evidence about its structure became available.· A scientific model differs from a replica (physical model) because it represents a phenomenon that cannot be observed directly.Teaching SuggestionsUse this slide as a review of the experiments that led up to the present-day view of the atom. Ask students to describe the characteristics of each atomic model and the discoveries that led to its modification. Make sure that students understand that the present-day model shows the most probable location of an electron at a single instant.Point out that most scientific models and theories go through an evolution similar to that of the atomic model. Modifications often must be made to account for new observations. Discuss why scientific models, such as the atomic models shown here, are useful in helping scientists interpret heir observations.QuestionsDescribe the discovery that led scientists to question John Dalton’s model of the atom ad to favor J.J. Thomson’s model.What experimental findings are the basis for the 1909 model of the atom?What shortcomings in the atomic model of Ernest Rutherford led to the development of Niels Bohr’s model?A friend tells you that an electron travels around an atom’s nucleus in much the same way that a planet revolves around the sun. Is this a good model for the present-day view of the atom? Why or why not?Another friend tells you that the present-day view of an electron’s location in the atom can be likened to a well-used archery target. The target has many holes close to the bull’s-eye and fewer holes farther from the center. The probability that the next arrow will land at a certain distance from the center corresponds to the number of holes at that distance. Is this a good model for the present-day view of the atom? Why or why not?Suppose that, it the future, an apparatus were developed that could track and record the path of an electron in an atom without disturbing its movement. How might this affect the present-day model of the atom? Explain your answer.How does developing a model of an atom differ from making a model of an airplane? How are these two kinds of models the same?Drawing on what you know in various fields of science, write a general statement about the usefulness of scientific models.Timeline: Wysession, Frank, Yancopoulos Physical Science Concepts in Action, Prentice Hall/Pearson, 2004 pg 1141803 John Daltonpictures atoms astiny, indestructibleparticles, with nointernal structure.1897 J.J. Thomson, a Britishscientist, discovers the electron,leading to his "plum-pudding"model. He pictures electronsembedded in a sphere ofpositive electric charge.1911 New ZealanderErnest Rutherford statesthat an atom has a dense,positively charged nucleus.Electrons move randomly inthe space around the nucleus.1926 Erwin Schrodingerdevelops mathematicalequations to describe themotion of electrons inatoms. His work leads tothe electron cloud model.1913 In Niels Bohr'smodel, the electrons movein spherical orbits at fixeddistances from the nucleus.1924 Frenchman Louisde Broglie proposes thatmoving particles like electronshave some properties of waves.Within a few years evidence iscollected to support his idea.1932 JamesChadwick, a Britishphysicist, confirms theexistence of neutrons,which have no charge.Atomic nuclei containneutrons and positivelycharged protons.1904 Hantaro Nagaoka, aJapanese physicist, suggeststhat an atom has a centralnucleus. Electrons move inorbits like the rings around Saturn.Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125
38 What the inside of your foldable should look like….
39 What the inside of your foldable should look like….