John Dalton's Modern Atomic Model
In Chapter 8 of Atomic Theory, we learn about John Dalton's groundbreaking proposal for a modern atomic model in 1800. Unlike previous atomic models, Dalton's was based on experimentation rather than
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About John Dalton's Modern Atomic Model
PowerPoint presentation about 'John Dalton's Modern Atomic Model'. This presentation describes the topic on In Chapter 8 of Atomic Theory, we learn about John Dalton's groundbreaking proposal for a modern atomic model in 1800. Unlike previous atomic models, Dalton's was based on experimentation rather than. The key topics included in this slideshow are . Download this presentation absolutely free.
Slide1Atomic TheoryChapter 8 The Composition of the atom
Slide2John Dalton• 1800 -Dalton proposed a modern atomic model based on experimentation not on pure reason. • All matter is made of atoms. • Atoms of an element are identical. • Each element has different atoms. • Atoms of different elements combine in constant ratios to form compounds. • Atoms are rearranged in reactions. • His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).
Slide31803 John Dalton• Dalton’s Model of the Atom: – Uniform Shape – Uniform Density – Indivisible • So what did Dalton’s model look like? • A simple design that promoted future research into atomic theory…
Slide4Discovering the Electron• He noticed a flash of light within one of the tubes. • Flash was produced by some form of radiation striking the light at the end of the tube. • There were rays (radiation) traveling from the cathode to the anode in the tube. • They called it the cathode ray b/c the ray of radiation originated from the cathode end of the tube. • Thank you Sir William Crookes!!!!!
Slide5The Cathode Ray Tube (CRT)Developed by Sir William Crookes in the late 1800s
Slide6Thank you Sir William Crookes!!!!!For your Accidental Discovery!!!!! 1879 • Discovery of cathode rays led to invention of the TV!!!! • TV and computer monitor images are formed as radiation from the cathode strikes the light producing chemicals that coat the backside of the screen.
Slide7JJ Thompson 1897• Using the CRT… Fluorescent Screen Electromagnets (turned off) Cathode (--) Anode (+) Beam of “light”
Slide8JJ Thompson 1897• When the magnets were turned on, the beam was pulled towards the + plate • What could Thompson conclude? + side -- side
Slide9•What did his experiment discover? • ELECTRONS! (negatively-charged particles) • How did the model of the atom change? JJ Thompson 1897 AKA The Chocolate-Chip Cookie Model
Slide10Robert Millikan 1909• Determined the charge of an electron. • Mass of an electron = 9.1 x 10 -28 g • Mass of an electron is extremely small.
Slide11Millikan’s Experiment• Measured the time it took for an electrically charged oil drop to rise a measured distance when subjected to an electric field • Measured the time it took electrically charged droplets to fall with no electric field
Slide12Oil Drop Experiment
Slide13Millikan’s Outcomes• Determined the charge on a single electron • Using the charge from Millikan and the charge-to-mass ratio from Thomson, many scientists determined the mass of an electron .
Slide14Discoveries from the CRT• Wilhelm Roentgen (1895) ? ● Discovered x-rays ● Killed his wife
Slide15Henri Becquerel 1896• Roentgen’s Discovery of X-rays provoked further research by many others, including Becquerel • Since fluorescent materials could be charged by X-rays, Henri wondered if naturally fluorescent minerals could give off X-rays…. • Like any good scientist, he set up a test…
Slide16Henri Becquerel 1896Photographic film sealed away
Slide17Henri Becquerel 1896The photographic paper was still exposed! The mineral contained Uranium! Serendipity- accidental discovery
Slide18Becquerel’s Outcomes • Concluded something in the sample itself must be capable of “fogging” the plates; the sample must give off some kind of ray without the influence of the sun • Rays were the products of radioactivity • 1896 - credited with the discovery of radioactivity ● Left a sample of uranium ore in a drawer with photo plates and there was fogging on the plates
Slide19Marie and Pierre Curie• French Scientists • Intrigued with Becquerel’s work • Studied radioactivity • Marie discovered the element POLONIUM
Slide20Ernst Rutherford 1898• After the discoveries of Becquerel and Thompson, Rutherford was dissatisfied with the atomic models and set out to disprove it. • Using Uranium, he and his lab assistants (Geiger and Marsden) set out…
Slide21Ernest Rutherford 1911• Studied how positively charged alpha particles interacted with solid matter. Conducted an experiment to see if alpha particles would be deflected as they passed through a thin foil of gold. Also known as Rutherford’s Gold Foil Experiment.
Slide22Ernest Rutherford’s Gold Foil Experiment1. A narrow beam of alpha particles was aimed at a thin sheet of gold foil. 2. A zinc sulfide coated screen surrounding the gold foil produced a flash of light whenever it was struck by an alpha particle. 1. Most all of the alpha particles passed straight through the gold foil, without deflection. 2. Some alpha particles were scattered at small angles. A few times they were deflected at very large angles .
Slide23Rutherford’s Gold Foil Conclusions1. Rutherford said plum pudding model was incorrect. 2. An atom consisted mostly of empty space through which the electrons move. 3. There was a tiny, dense region, called the nucleus, centrally located within the atom that contained all of an atom’s positive charge and almost all of its’ mass.
Slide24Planetary Motion Model• Electrons orbit around the nucleus like planets orbit around the sun • The nucleus held only protons (now)
Slide25Hans Geiger• Student of Rutherford • Spent long hours counting the particles that hit the screen • Created the first electric particle counter - The GEIGER counter • Determined that alpha particles had 2 p + and 2n 0 (1908)
Slide26Irene Curie-Joliot & FredericJoliot • Bombarded Be with alpha particles - formed a beam of energy with great power which was able to penetrate metals • Thought it was new form of energy - thought it was gamma rays
Slide27James Chadwick• Found new beam of energy was unaffected by magnetic fields - so it was neutral • Particles moved at 1/10 the speed of light - so it was NOT radiant energy - but must be particles • The new particles had approximately the same mass as a proton - but they had no charge • Credited with the discovery of the NEUTRON
Slide28After Chadwick• After neutrons were discovered - isotopes of various elements were discovered • We will come back and pick up our story in a little bit.