Rutherford Model of the Atom

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Rutherford Model of the Atom

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Rutherford Model of the Atom:

Rutherford Model of the Atom (The modern view of the atom was developed by Ernest Rutherford)

Ernest Rutherford (1871-1937):

Ernest Rutherford (1871-1937) Learned physics in J.J. Thomson’ lab. Noticed that ‘alpha’ particles were sometime deflected by something in the air. Gold-foil experiment Rutherford PAPER Animation by Raymond Chang – All rights reserved.

Rutherford ‘Scattering’:

Rutherford ‘Scattering’ In 1909 Rutherford undertook a series of experiments He fired a (alpha) particles at a very thin sample of gold foil According to the Thomson model the a particles would only be slightly deflected Rutherford discovered that they were deflected through large angles and could even be reflected straight back to the source particle source Lead collimator Gold foil a q

Rutherford’s Apparatus:

Rutherford’s Apparatus beam of alpha particles radioactive substance gold foil circular ZnS - coated fluorescent screen Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120 Rutherford received the 1908 Nobel Prize in Chemistry for his pioneering work in nuclear chemistry.

Rutherford’s Apparatus:

Rutherford’s Apparatus Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120 beam of alpha particles radioactive substance fluorescent screen circular - ZnS coated gold foil

Geiger-Muller Counter:

Geiger-Muller Counter Speaker gives “click” for each particle Window Particle path Argon atoms Hans Geiger

Geiger Counter:

Geiger Counter e- e- e- e- + + + + Metal tube (negatively charged) Ionization of fill gas takes place along track of radiation Ionizing radiation path Window Atoms or molecules of fill gas Central wire electrode (positively charged) Wilbraham, Staley, Matta, Waterman, Chemistry , 2002, page 857 Free e - are attracted to (+) electrode, completing the circuit and generating a current. The Geiger counter then translates the current reading into a measure of radioactivity. Speaker gives “click” for each particle (+) (-)

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Lead block Polonium Gold Foil Florescent Screen California WEB

What He Expected:

What He Expected The alpha particles to pass through without changing direction (very much) Because The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles California WEB

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What he expected… California WEB

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What he expected…

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Because he thought the mass was evenly distributed in the atom. - - - - -

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Because, he thought the mass was evenly distributed in the atom - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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What he got… richocheting alpha particles

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What he got… richocheting alpha particles

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The Predicted Result: expected path expected marks on screen mark on screen likely alpha particle path Observed Result:

Interpreting the Observed Deflections:

Interpreting the Observed Deflections Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120 . . . . . . . . . . . . . . gold foil deflected particle undeflected particles . . beam of alpha particles .

Density and the Atom:

Density and the Atom Since most of the particles went through, the atom was mostly empty. Because the alpha rays were deflected so much, the positive pieces it was striking were heavy. Small volume and big mass = big density This small dense positive area is the nucleus California WEB

Rutherford Scattering (cont.):

Rutherford Scattering (cont.) Rutherford interpreted this result by suggesting that the a particles interacted with very small and heavy particles Particle bounces off of atom? Particle attracts to atom? Particle goes through atom? Particle path is altered as it passes through atom? . Case A Case B Case C Case D

Table: hypothetical description of alpha particles:

Table: hypothetical description of alpha particles alpha rays don’t diffract alpha rays deflect towards a negatively charged plate and away from a positively charged plate alpha rays are deflected only slightly by an electric field; a cathode ray passing through the same field is deflected strongly ... alpha radiation is a stream of particles ... alpha particles have a positive charge ... alpha particles either have much lower charge or much greater mass than electrons observation hypothesis (based on properties of alpha radiation) Copyright © 1997-2005 by Fred Senese

Explanation of Alpha-Scattering Results:

Explanation of Alpha-Scattering Results Plum-pudding atom + + + + + + + + - - - - - - - - Alpha particles Nuclear atom Nucleus Thomson’s model Rutherford’s model

Results of foil experiment if plum-pudding had been correct.:

Results of foil experiment if plum-pudding had been correct. Electrons scattered throughout positive charges Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57 + + + + + + + + - - - - - - - -

Interpreting the Observed Deflections:

Interpreting the Observed Deflections Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120 . . . . . . . . . . . . . . gold foil deflected particle undeflected particles . . beam of alpha particles .

Rutherford’s Gold-Leaf Experiment Conclusions: Atom is mostly empty space Nucleus has (+) charge Electrons float around nucleus:

Rutherford’s Gold-Leaf Experiment Conclusions: Atom is mostly empty space Nucleus has (+) charge Electrons float around nucleus Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120

Rutherford’s Experiment:

Rutherford’s Experiment Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56

Actual Results of Gold-Leaf Experiment:

Actual Results of Gold-Leaf Experiment Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57 n +

The Rutherford Atom:

The Rutherford Atom Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57 n + - - - - - - - - - -

PowerPoint Presentation:

This is the modern atom model. Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons. This picture is quite distorted. If we drew the atom to scale and made protons and neutrons a centimeter in diameter, then the electrons and quarks would be less than the diameter of a hair and the entire atom's diameter would be greater than the length of thirty football fields! 99.999999999999% of an atom's volume is just empty space! Website “ The Particle Adventure ”

Scale of the atom.:

While an atom is tiny, the nucleus is ten thousand times smaller than the atom and the quarks and electrons are at least ten thousand times smaller than that. We don't know exactly how small quarks and electrons are; they are definitely smaller than 10 -18 meters, and they might literally be points, but we do not know. It is also possible that quarks and electrons are not fundamental after all, and will turn out to be made up of other, more fundamental particles. (Oh, will this madness ever end?) Scale of the atom. Website “ The Particle Adventure ”

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Physicists have developed a theory called The Standard Model that explains what the world is and what holds it together. It is a simple and comprehensive theory that explains all the hundreds of particles and complex interactions with only: 6 quarks . 6 leptons . The best-known lepton is the electron. Force carrier particles , like the photon. We will talk about these particles later. All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles. The Standard Model is a good theory . Experiments have verified its predictions to incredible precision, and all the particles predicted by this theory have been found. But it does not explain everything. For example, gravity is not included in the Standard Model. Website “ The Particle Adventure ”

Discovery of the electron:

Discovery of the electron 1807 Davy suggested that electrical forces held compound together. 1833 Faraday related atomic mass and the electricity needed to free an element during electrolysis experiments. 1891 Stoney proposed that electricity exists in units he called electrons. 1897 Thomson first quantitatively measured the properties of electrons.

Coulomb’s Law:

Coulomb’s Law Why don’t electrons collide while moving around the outside of atom? Why can’t we add protons to nucleus? When an ion forms: cation…gain protons or lose electrons ? anion…lose protons or gain electrons ? Coulomb’s law Both negative charges (repel each other) Hard to hit small nucleus (+) will repel (+)

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Hit moth driving car – no change in car direction Hit deer – car changes direction Alpha particle Large angle of deflection, must have hit massive object! moth deer Gold Atom

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Hit moth driving car – no change in car direction Hit deer – car changes direction Alpha particle Large angle of deflection, must have hit massive object! moth deer Gold Atom

Force:

Force Definite proportions H 2 O 2 H @1 g/mol = 2 g 1 O @ 16 g/mol = 16 g 1:8 H:O by mass Coulomb’s law

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