Atom3 021611

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 answer

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PROTON - +1

ELECTRON - -1

NEUTRON - 0

NUCLEUS - positive

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Announce-mintsFebruary 14- 18

Wed - the atom; course content letter DUE

Thurs - the atom

Fri - the atom

Mon Feb 21st: NO SCHOOL!

History of the atomic model

Democritus “atoms are indivisible, solid spheres”

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John DaltonQuickTime™ and a

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The Father of the Atom

How were electrons discovered?

J. J. Thomson

Used a CATHODE RAY TUBE to discover electrons

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How were electrons discovered?

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are needed to see this picture.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

cathode

anode

Thomson’s atomic model(chocolate chip cookie dough)

J. J. Thomson

Named the negative particles “ELECTRONS”

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Positively charge sphere with negative electrons throughout the atom

Thomson’s atomic model(chocolate chip cookie dough)

J. J. Thomson

Named the negative particles “ELECTRONS”

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Positively charge sphere with negative electrons throughout the atom

How was the nucleus discovered?

Ernest Rutherford

Conducted the Gold Foil Experiment- was a research student of J.J. Thomson

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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?

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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

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Practice

Lesson 1 WS (due today) Textbook p. 179:1-5

Answer the questions in COMPLETE SENTENCES

Finish for HW (due 2/17)

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