Presentation on theme: "Chapter 8 The Composition of the atom"— Presentation transcript:
1 Chapter 8 The Composition of the atom Atomic TheoryChapter 8The Composition of the atom
2 John 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).
3 1803 John Dalton Dalton’s Model of the Atom: Uniform ShapeUniform DensityIndivisibleSo what did Dalton’s model look like?A simple design that promoted future research into atomic theory…
4 Discovering 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!!!!!
5 The Cathode Ray Tube (CRT) Developed by Sir William Crookes in the late 1800s
6 Thank 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.
7 Electromagnets (turned off) JJ Thompson 1897Using the CRT…Fluorescent ScreenElectromagnets (turned off)Cathode (--)Anode (+)Beam of “light”
8 JJ Thompson 1897When the magnets were turned on, the beam was pulled towards the + plateWhat could Thompson conclude?+ side-- side
9 AKA The Chocolate-Chip Cookie Model JJ Thompson 1897What did his experiment discover?ELECTRONS! (negatively-charged particles)How did the model of the atom change?AKA The Chocolate-Chip Cookie Model
10 Robert Millikan 1909Determined the charge of an electron.Mass of an electron = 9.1 x gMass of an electron is extremely small.
11 Millikan’s Experiment Measured the time it took for an electrically charged oil drop to rise a measured distance when subjected to an electric fieldMeasured the time it took electrically charged droplets to fall with no electric field
13 Millikan’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.
14 Discoveries from the CRT Wilhelm Roentgen (1895)?●Discovered x-rays●Killed his wife
15 Henri Becquerel 1896Roentgen’s Discovery of X-rays provoked further research by many others, including BecquerelSince 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…
16 Photographic film sealed away Henri Becquerel 1896Photographic film sealed away
17 Henri Becquerel 1896 The photographic paper was still exposed! The mineral contained Uranium!Serendipity- accidental discovery
18 Becquerel’s Outcomes● Left a sample of uranium ore in a drawer with photo plates and there was fogging on the platesConcluded 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 sunRays were the products of radioactivitycredited with the discovery of radioactivity
19 Marie and Pierre Curie French Scientists Intrigued with Becquerel’s workStudied radioactivityMarie discovered the element POLONIUM
20 Ernst Rutherford 1898After 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…
21 Ernest Rutherford 1911Studied 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.
22 Ernest Rutherford’s Gold Foil Experiment 1. A narrow beam of alpha particles was aimedat a thin sheet ofgold 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.A few times they were deflected at very large angles.2. Some alpha particles were scattered at small angles.
23 Rutherford’s Gold Foil Conclusions 1. 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.
24 Planetary Motion Model Electrons orbit around the nucleus like planets orbit around the sunThe nucleus held only protons (now)
25 Hans Geiger Student of Rutherford Spent long hours counting the particles that hit the screenCreated the first electric particle counter - The GEIGER counterDetermined that alpha particles had 2 p+ and 2n0 (1908)
26 Irene Curie-Joliot & Frederic Joliot Bombarded Be with alpha particles - formed a beam of energy with great power which was able to penetrate metalsThought it was new form of energy - thought it was gamma rays
27 James Chadwick Credited with the discovery of the NEUTRON Found new beam of energy was unaffected by magnetic fields - so it was neutralParticles moved at 1/10 the speed of light - so it was NOT radiant energy - but must be particlesThe new particles had approximately the same mass as a proton - but they had no chargeCredited with the discovery of the NEUTRON
28 After ChadwickAfter neutrons were discovered - isotopes of various elements were discoveredWe will come back and pick up our story in a little bit.