Todays PPT
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Transcript of Todays PPT
Wednesday, February 16, 2011
Agenda• Welcome• Announcements• Turn in Sci WB p39-40• The atomic model:
electrons & the nucleus• Lesson 1 WS (due today)• HW: Textbook p. 179:1-5
Warm Up
Draw & label an atom; what are the
charges of the parts?
I love science
Warm up answerPROTON - +1
ELECTRON - -1
NEUTRON - 0
NUCLEUS - positive
Announce-mintsFebruary 14- 18
Wed - the atom; course content letter DUEThurs - the atomFri - the atomMon Feb 21st: NO SCHOOL!
History of the atomic model
Democritus “atoms are indivisible, solid spheres”
John DaltonThe Father of the Atom
How were electrons discovered?
J. J. ThomsonUsed a CATHODE RAY TUBE to discover electrons
How were electrons discovered?
Thomson’s experiment1. Turned on cathode rayThe ray flows from cathode to the anode2. Put a positive plate on top and negative plate on bottomObserved ray bend towards positive plateThe ray must have negative particles
Positive plate
Negative plate
cathodeanode
Thomson’s atomic model(chocolate chip cookie dough)
J. J. ThomsonNamed the negative particles “ELECTRONS”
Positively charge sphere with negative electrons throughout the atom
Thomson’s atomic model(chocolate chip cookie dough)
J. J. ThomsonNamed the negative particles “ELECTRONS”
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Positively charge sphere with negative electrons throughout the atom
How was the nucleus discovered?
Ernest RutherfordConducted the Gold Foil Experiment
- was a research student of J.J. Thomson
How was the nucleus discovered?
1. Alpha particles shot through gold foil
2. Detected by screen around the foil
EXPECTEDUNEXPECTED
3. Particles were detected in unexpected places.
How was the nucleus discovered?
Rutherford expected particles to crash through gold foil w/ little change in direction
Some particles bounced off the gold foil in ways that were not predicted by Thomson’s model
Rutherford’s Atomic Model
An atom is mostly empty space
Most of the mass is in the center of an atom
Positive charge is concentrated in the center
Electrons orbit the nucleus atany given distance from nucleus
Practice Lesson 1 WS (due today) Textbook p. 179:1-5
Answer the questions in COMPLETE SENTENCES
Finish for HW (due 2/17)