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)