Journey Through Atomic Models: From Thomson's Plum Pudding to Rutherford's Gold Foil Experiment
Road trip so far:
Classic chemistry:
Chapters 1-5
Mole reasoning
Reactions
Gas=>
stoichiometries
Ahead of us (and your
reading):
What’s inside the atomic
cookie (pp. 50-53 + Ch.7)
•
Molecular models (Ch. 8)
Today’s
S
tudent
L
earning
O
bjective (
SLO
):
Translation:
What’s inside the atomic
cookie….
and
how
do we know this ???
SLO#2
Students should be able to provide a
basic description of the atomic and
electronic structures of atoms .
The first try at mapping the atomic cookie
:
J. J
.
Thomson’s
`
Plum Pudding Model
’ :
1897
(see text p.50 )
J.J’s
`
C
athode
R
ay
T
ube’ (
CRT
)*
J.J. Thomson
Cavendish Labs,
Cambridge UK
*
factoid:
Thomson
was said to be astonishingly bad in the lab and
fumble-fingered; the
CRT
was made by a gifted glassblower,
E. Everett
Schematic of Thomson’s critical experiments
Atomic structure: try 1 –
Thomson’s atom
(continued)
2) e
-
beam from cathode (- plate)
accelerated towards (+) plate
1)Battery voltage
tears something
(e-)
away from
metal
cathode
3) Fields applied and results observed on `TV’ screen
Basic result of
Thomson’s
CRT
experiments:
All the materials subjected to high voltage in the tube
vomited the same kind of `
negative
’ particles-dubbed
the
electron.
Thomson’s
Conjecture from his
CRT
experiments
If all matter has
negative electrons
, there must be a
counterbalancing
positive glue
that
sticks
to
and
neutralizes
the electrons’
negative
charge (since matter
is normally
neutral
).
Atomic structure: try 1-
Thomson’s atom
(continued)
1
J.J. Thomson
Cathode Rays
,
Philosophical Magazine
44
, 295 (1897)
Thompson’s
conjecture
morphed into the first
experimentally derived atomic model:
“The
Plum Pudding
Model”
1
Atomic structure: try 1 –
Thomson’s
atom (continued)
Cookie
metaphor -if
you’ve never
had
plum
pudding
Testing the plum pudding atom:
Rutherford’s
gold foil
experiment
(1910) (
see also: page 52 of text)
Ernst Rutherford
Physical Laboratory
Manchester University, UK
*Factoid: it’s really his students-
Geiger
and
Marsden-
who
machine the device and do the measurements.
Rutherford’s
Gold foil
apparatus*
Atomic structure: testing
Thomson’s Plum Pudding atomic model
(continued)
Gold Foil
Experiment lore
1)
Marie Curie supplied the radon =
source.
2)
It required ~ 1 hour sitting in absolute dark to condition eyes.
3)
You could only observe scintillations for 1-2 minutes before
desensitizing.
Schematic of
Rutherford’s
`
gold foil
’
apparatus
•
Alpha (
)
particles=He
+
Microscope
Rotated to detect
scintillations
ZnS screen is a scintillating surface
Atomic structure: testing
Thomson’s Plum Pudding Atomic Model
(continued)
Other Facts about the
Gold Leaf Experiment
rarely mentioned:
•
particles move crazy fast:
velocity ~
0.1c ~7*10
7
mph
(can get to NYC from here in ~0.01 sec
)
•
The gold foil is crazy thin:
~ 8.6*10
-6
cm thick
(~1/3000 the thickness of cheap toilet paper )
•
particles are crazy overweight compared to the
electrons (e-) in a gold atom:
~800X heavier than all 79
e-
in gold atom
Atomic structure: testing
Thomson’s Plum Pudding Model
(continued):
Reminder of the
Plum Pudding Model
being tested
Given the preceding facts, predict how the
particles will behave after striking the gold foil
if
the structure of gold is as described in Thomson’s
Plum Pudding model .
A.
Bounce straight backwards
off the foil like a baseball
hitting a wall.
B.
Punch through the foil like
it wasn’t there.
C.
Scatter off the foil
randomly in all directions.
Plum Pudding model
predicts
the massive
particles
will
pass ~un-deflected through gold foil made of diffuse matter
particles
•
Rutherford’s
observations
mostly
agree with above.
Gold foil
•
But
sometimes
a few curve off significantly…
•
And once and in a great while
, one bounces back. !
Pictorial summary of results of gold foil experiment
Geiger H. & Marsden E
., On the Diffuse Reflectance of
-Particles
Proceedings of the Royal Society, Series A
82: 495–500 (1909)
Seminal publication on results:
Atomic structure: testing
Thomson’s Plum Pudding Atomic Model
(continued)
“
Like firing a
howitzer at tissue
paper and having
the shell bounce
back !!”
Rutherford’s famous `take’ on Marsden and
Geiger’s results:
Atomic structure: testing
Thomson’s Plum Pudding Atomic Model
(continued)
Which model below best explains the
gold foil scattering data?
A.
Thin, dense
electron
ring
around large, dense ball of
positives
.
B.
diffuse, continuous ball of
electrons
around tiny, dense
ball of
positives.
C.
Inner thin, dense
positive
ring surrounded by outer
thin,dense
electron
ring.
E. Rutherford, F.R.S.
The Scattering of α and β Particles by
Matter and the Structure of the Atom
Philosophical Magazine
Series 6, vol. 21, p. 669-688 (1911)
Rutherford’s
Atom:1911
The Second Experimentally-Based Model of the Atom
Atomic structure:
Rutherford’s
Atomic Model
Electrons
in
diffuse cloud
around tiny (but
massive) positive
charged
nucleus.
Dimensions of Rutherford atomic model
*
*derived from statistics of gold leaf scattering experiment
•
Nuclear radius
~10
-15
meters
•
Electronic cloud radius
~ 10
-10
meters
proton
1.67*10
-30
neutron
1.67*10
-30
electron
9.11*10
-34
Masses of subatomic pieces
**
1
1
0.0005
•
Electronic radius/
Nuclear radius
~ 10
+5
** from J. Aston development of mass spectroscopy at
Cavendish Labs (w/Rutherford as its’ new Director)
Atom dimensions in familiar terms.
Metaphor 1
Baseball as
nucleus
Old Yankee Stadium, the Bronx
PS:
Yanks rule
Boston drools
Electrons
start here
(~
2.4
miles past
cheap seats)
3”
Nucleus(+)
~ dimension of Rutherford’s
electronic cloud (-) (2.4 mile
radius from baseball nucleus
)
Atom dimensions in familiar terms
Example 2
U-Do-It
•
Super
Target
store in Omaha, Neb., is the
nucleus
•
Assume the radius of the store is 75 m (0.75 km)
•
Assume
electronic cloud
is 100,000X larger in diameter
Nucleus= Super Target
store in Omaha
Atom dimensions in familiar terms…
U-Do-it
Example 2: where is electron cloud?
Chicago NYC Paris Beijing
Which city best defines the boundary of
Rutherford’s electron cloud if a Super Target
store in Omaha is the nucleus ?
A.
Chicago:7*10
2
km away
B.
NYC: 2*10
3
km away
C.
Paris: 7*10
3
km away
D.
Beijing 1.6*10
4
km away
Store radius = 75 m
Electron radius
=100,000
Nuclear radius
Paris
Nucleus=Super Target
store in Omaha
•
Pencil dot + string (clickers)
•
Penny analogy (clickers)
•
paper + scissors (board work)
•
Pea=nucleus
volume of electrons
(board work)
OTHER METAPHORS TO `GRASP’
ATOMIC DIMENSIONS
If a pencil dot, which has a radius of~ 0.02 cm, is
the nucleus, how many cm away are the electrons ?
A.
200,000 cm
B.
20,000 cm
C.
2000 cm
D.
200 cm
E.
I have no clue
If an electron is a penny , how much money do
you need to equal the mass of 1 proton ? (mass of
proton/mass of electron ~1836)
A.
$18.36
B.
$ 1836
C.
$1.83(6)
D.
0.0005 $
E.
No clue
Volume comparison
Nuclear volume=
1 pea (~0.065 cm
3
)
Electron cloud volume ~ volume
of water in Honeoye Lake, NY
(10
15
times pea volume)
The electron cloud volume is 10
15
times bigger
than the nuclear volume
Explore the evolution of atomic models starting with J.J. Thomson's Plum Pudding Model in 1897, where the discovery of electrons led to the belief of a positive "glue." Follow the progression to Ernest Rutherford's Gold Foil Experiment in 1910, challenging the Plum Pudding Model and unveiling the nucleus.
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Presentation Transcript
Road trip so far: Classic chemistry: Chapters 1-5 Mole reasoning Reactions Gas=> stoichiometries Ahead of us (and your reading): What s inside the atomic cookie (pp. 50-53 + Ch.7) Molecular models (Ch. 8)
Todays Student Learning Objective (SLO): SLO#2 Students should be able to provide a basic description of the atomic and electronic structures of atoms . Translation: What s inside the atomic cookie . and how do we know this ???
The first try at mapping the atomic cookie: J. J. Thomson s `Plum Pudding Model : 1897 (see text p.50 ) J.J. Thomson Cavendish Labs, Cambridge UK J.J s `Cathode Ray Tube (CRT)* *factoid: Thomson was said to be astonishingly bad in the lab and fumble-fingered; the CRT was made by a gifted glassblower, E. Everett
Atomic structure: try 1 Thomsons atom (continued) Schematic of Thomson s critical experiments 1)Battery voltage tears something (e-) 2) e- beam from cathode (- plate) accelerated towards (+) plate http://session.masteringchemistry.com/problemAsset/1070873/24/BLB-1070873-CRT_v2.jpg away from metal cathode 3) Fields applied and results observed on `TV screen
Atomic structure: try 1-Thomsons atom (continued) Basic result of Thomson s CRT experiments: All the materials subjected to high voltage in the tube vomited the same kind of `negative particles-dubbed the electron. Thomson s Conjecture from his CRT experiments If all matter has negative electrons, there must be a counterbalancing positive glue that sticks to and neutralizes the electrons negative charge (since matter is normally neutral).
Atomic structure: try 1 Thomsons atom (continued) Thompson s conjecture morphed into the first experimentally derived atomic model: The Plum Pudding Model 1 http://images.tutorvista.com/content/atoms-and-nuclei/plum-pudding-model.jpeg http://t2.gstatic.com/images?q=tbn:ANd9GcTlP2d6KFMFmGC5cUWnKpqotpPxc06_WbQ078Oul47_RgeYtky-fg Cookie metaphor -if you ve never had plum pudding 1 J.J. Thomson Cathode Rays, Philosophical Magazine44, 295 (1897)
Testing the plum pudding atom: Rutherfords gold foil experiment (1910) (see also: page 52 of text) Ernst Rutherford Physical Laboratory Manchester University, UK http://myweb.usf.edu/~mhight/rutherfordlab.jpg http://137.193.61.237/images/theory_abb1.jpg Rutherford sGold foil apparatus* *Factoid: it s really his students-Geiger and Marsden-who machine the device and do the measurements.
Atomic structure: testing Thomsons Plum Pudding atomic model (continued) Schematic of Rutherford s `gold foil apparatus Microscope Rotated to detect scintillations http://www.antonine-education.co.uk/Image_library/Physics_5/Nuclear_physics/alpha.gif Alpha ( ) particles=He+ ZnS screen is a scintillating surface Gold Foil Experiment lore 1) Marie Curie supplied the radon = source. 2) It required ~ 1 hour sitting in absolute dark to condition eyes. 3) You could only observe scintillations for 1-2 minutes before desensitizing.
Atomic structure: testing Thomsons Plum Pudding Atomic Model(continued) Other Facts about the Gold Leaf Experiment rarely mentioned: particles move crazy fast: velocity ~ 0.1c ~7*107 mph (can get to NYC from here in ~0.01 sec) particles are crazy overweight compared to the electrons (e-) in a gold atom: ~800X heavier than all 79 e- in gold atom The gold foil is crazy thin: ~ 8.6*10-6 cm thick (~1/3000 the thickness of cheap toilet paper )
Atomic structure: testing Thomsons Plum Pudding Model (continued): Reminder of the Plum Pudding Model being tested http://images.tutorvista.com/content/atoms-and-nuclei/plum-pudding-model.jpeg
Given the preceding facts, predict how the particles will behave after striking the gold foil if the structure of gold is as described in Thomson s Plum Pudding model . A. Bounce straight backwards off the foil like a baseball hitting a wall. B. Punch through the foil like it wasn t there. C. Scatter off the foil randomly in all directions. 78% 20% 2% Scatter off the fo.. Punch through... Bounce straigh...
Plum Pudding model predicts the massive particles will pass ~un-deflected through gold foil made of diffuse matter particles http://images.tutorvista.com/content/atoms-and-nuclei/plum-pudding-model.jpeg Rutherford s observationsmostly agree with above. Butsometimesa few curve off significantly And once and in a great while, one bounces back. ! Gold foil
Atomic structure: testing Thomsons Plum Pudding Atomic Model(continued) Pictorial summary of results of gold foil experiment http://mysite.verizon.net/kdrews47/introterms/goldfoil.gif Seminal publication on results: Geiger H. & Marsden E., On the Diffuse Reflectance of -Particles Proceedings of the Royal Society, Series A 82: 495 500 (1909)
Atomic structure: testing Thomsons Plum Pudding Atomic Model(continued) Rutherford s famous `take on Marsden and Geiger s results: Like firing a howitzer at tissue paper and having the shell bounce back !!
Which model below best explains the gold foil scattering data? 33% 33% 33% A. Thin, dense electron ring around large, dense ball of positives. B. diffuse, continuous ball of electrons around tiny, dense ball of positives. C. Inner thin, dense positive ring surrounded by outer thin,dense electron ring. Thin, dense... diffuse, con... Inner thin, ...
Atomic structure: Rutherfords Atomic Model Rutherford s Atom:1911 The Second Experimentally-Based Model of the Atom Electrons in diffuse cloud around tiny (but massive) positive charged nucleus. E. Rutherford, F.R.S. The Scattering of and Particles by Matter and the Structure of the Atom Philosophical Magazine Series 6, vol. 21, p. 669-688 (1911)
Dimensions of Rutherford atomic model* *derived from statistics of gold leaf scattering experiment Nuclear radius Electronic cloud radius ~ 10-10 meters Electronic radius/Nuclear radius ~ 10+5 ~10-15 meters Masses of subatomic pieces** Subatomic piece proton neutron electron ** from J. Aston development of mass spectroscopy at Cavendish Labs (w/Rutherford as its new Director) Mass (g) 1.67*10-30 1.67*10-30 9.11*10-34 Relative mass 1 1 0.0005
Atom dimensions in familiar terms. Metaphor 1 Electrons start here (~2.4 miles past cheap seats) 3 Baseball as nucleus PS: Yanks rule Boston drools Old Yankee Stadium, the Bronx
http://www.aaccessmaps.com/images/maps/us/ny/nyc_area_hwy/nyc_area_hwy.gifhttp://www.aaccessmaps.com/images/maps/us/ny/nyc_area_hwy/nyc_area_hwy.gif Nucleus(+) ~ dimension of Rutherford s electronic cloud (-) (2.4 mile radius from baseball nucleus)
Atom dimensions in familiar terms Example 2 U-Do-It Super Target store in Omaha, Neb., is the nucleus Assume the radius of the store is 75 m (0.75 km) Assume electronic cloud is 100,000X larger in diameter
Atom dimensions in familiar terms U-Do-itExample 2: where is electron cloud? Chicago NYC Paris Beijing Nucleus= Super Target store in Omaha
Which city best defines the boundary of Rutherford s electron cloud if a Super Target store in Omaha is the nucleus ? A. Chicago:7*102 km away B. NYC: 2*103 km away C. Paris: 7*103 km away D. Beijing 1.6*104 km away 0% 0% 0% 0% Store radius = 75 m Electron radius =100,000 Nuclear radius NYC: 2*103 km away Chicago:7*102 km away Paris: 7*103 km away Beijing 1.6*104 km away
Paris Nucleus=Super Target store in Omaha
OTHER METAPHORS TO `GRASP ATOMIC DIMENSIONS Pencil dot + string (clickers) Penny analogy (clickers) paper + scissors (board work) Pea=nucleus volume of electrons (board work)
If a pencil dot, which has a radius of~ 0.02 cm, is the nucleus, how many cm away are the electrons ? A. 200,000 cm B. 20,000 cm C. 2000 cm D. 200 cm E. I have no clue 20% 20% 20% 20% 20% 2000 cm 200 cm 20,000 cm 200,000 cm I have no clue
If an electron is a penny , how much money do you need to equal the mass of 1 proton ? (mass of proton/mass of electron ~1836) A. $18.36 B. $ 1836 C. $1.83(6) D. 0.0005 $ E. No clue 20% 20% 20% 20% 20% $18.36) $1,836) 0.0005 $ $1.83(6) No clue
Volume comparison The electron cloud volume is 1015 times bigger than the nuclear volume Electron cloud volume ~ volume of water in Honeoye Lake, NY (1015 times pea volume) Nuclear volume= 1 pea (~0.065 cm3)
