Transcript Honors Atomic Theory Power Point

History of
Atomic Theory
Chapter 5 - Part 2
Objectives - 1
List the 4 parts of Dalton’s Atomic Theory ad
explain its significance to the history of modern
atomic theory.
Diagram and explain the significance of a
Crooke’s Tube. Explain how the beam must have
been negatively charged particles.
Explain how Thomson discovered the existence of
the proton, the electron, and found the charge-tomass ratio of the electron.
Explain and draw a picture of the Plum Pudding
Model.
Objectives - 2
Explain and draw a picture of Millikan’s Oil Drop
Experiment.
Explain how the Oil Drop Exp. lead to the
discovery of the charge on the electron.
Explain how a fundamental principle of the ODE
was “like charges repel.”
State the discovery of William Roentgen.
State the discovery of Henri Becquerel.
Democritus of Abdera
Democritus of Abdera
Ancient Greece - 4th century BC
first suggested the existence of tiny
fundamental particles that make up matter.
atoms = indestructible
did not agree with the “current” sci theory - but
did not explain chemical behavior - and lacked
experimental support.
John Dalton
John Dalton
1766-1844
Eaglesfield, England
Father of modern atomic theory
Pro: advance in the description and nature of
chemical reactions.
Con: did not hold up when subatomic particles
were disovered
Dalton’s Atomic Theory
1. All elements are composed of tiny individual
particles - called atoms.
2. All matter is composed of combinations of
these atoms.
3. Atoms of different elements are different.
4. Atoms of the same element have the same
size, mass, and form.
Dalton’s Atom
The atom is a solid
indestructible
sphere.
William Crookes
William Crookes
1832-1919
British physicist
investigated why gases glow
Crookes’ Tube
Crookes’ Experiment
used a partially evacuated tube with a low
pressure gas and ran a current through it
power on: a green glow was emitted as a
beam of light ran across the tube
If the charge on the plates as switched . . .
Crookes’ Outcomes
It was a beam of particles?
How did he know?
Determined the particles had a negative
charge - due to . . .
Created a cathode ray tube (also called a
Crookes Tube)
This was the precursor to the TV tube - Thank
you Crookes!!!
JJ Thomson
JJ Thomson
1856-1940
British physicist
continued Crookes work
Experiment: applied an electric field which
bent the light inside the tube back to a straight
path and was able to measure this field.
Thomson’s Outcomes
discovered the electron
used the strength of the field was able to
determine the charge-to-mass ratio of this
negative particle beam - now so named
determined the existence of the proton
(because of neutrality)
Thomson’s Model
Plum Pudding Model
Negatively charged
electrons embedded
in a positive mass of
proton”ness”
JJ’s Pros & Cons
Pro: did explain some of the electrical nature
of matter.
Con: did not say anything about the number of
charged particles or their arrangement.
Won NOBEL PRIZE in 1906
Robert Millikan
Millikan &
Einstein
Robert Millikan
1868-1953
US Physicist
NOBEL PRIZE 1932
Oil Drop Experiment
Millikan’s Outcomes
determined the charge on a single electron
using the charge-to-mass ratio from Thomson,
many scientists determined the mass of an
electron
Wilhelm
Roentgen
William Roentgen
1845-1923
Discovered x-rays
killed his wife
Henri Becquerel
Henri Becquerel
1852-1908
French scientist
Left a sample of uranium ore in a drawer with
glass photo plates and there was fogging on
the plates
serendipity
Becquerel’s outcomes
concluded 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 sun
rays were the product of radioactivity
1896 - credited with the discovery of
radioactivity
Marie &
Pierre
Curie
Marie & Pierre Curie
Pierre, Pierre’s Assistant,
and Marie Curie
Pierre & Marie Curie
The Curie Family:
Pierre, Marie,
Irene, and
Grandfather Curie
Marie & Pierre Curie
French physicists
intrigued with Becquerel’s work
studied radioactivity
Marie discovered POLONIUM
Ernest Rutherford
Ernest Rutherford
1871-1937
New Zealand
discovered the nucleus of the atom
Planetary Motion Model
Gold Foil Experiment
Gold Foil Experiment - 2
A beam of alpha particles was directed at a
thin sheet of gold foil with a fluorescent screen
around it.
Most of the alpha particles went straight
through it - or had very little deflection.
A few were deflected back at very sharp
angles.
A 15-inch shell fired at a piece of tissue paper
and it came back and hit you.
Rutherford concludes...
Atoms have almost all of their mass
concentrated in a very small positively charged
region = the nucleus
The nucleus is surrounded by electrons which
are at a relatively large distance.
Why did the electrons not crash into the
nucleus in Rutherford’s model?
Planetary Motion Model
Electrons orbit
around the
nucleus like
planets orbit
around the sun.
The nucleus held
(only) protons (for
the time being).
Hans
Geiger
Hans Geiger
Student of Rutherford
He was one of the people who had to spend
long hours (in mostly darkness) counting the
particles that hit the screen.
Created the first electrical particle
counter - The Geiger counter
Geiger’s contributions
Determined that alpha particles were made up
of 2 protons and 2 neutrons. (1908)
This gives an alpha particle a mass number of
??? and a nuclear charge of ???.
Geiger - Rutherford’s
student
Curie-Joliot & Joliot
Irene Curie-Joliot
& Frederic Joliot
Bombarded beryllium with alpha particles which created a beam of energy that had great
power. It was able to penetrate metals.
They thought it was a new form of energy; they
thought it was gamma rays.
James Chadwick
James
Chadwick
James Chadwick
1891-1974
British physicist and chemist
Found the Curie-Joliot beam of energy was
unaffected by magnetic fields - meaning it
must be neutral.
Particles moved at 1/10 the speed of light - so
it was NOT radiant energy - it must be
PARTICLES
Chadwick’s Particles
The new particles had approximately the same
mass as a proton - but these new particles had
NO CHARGE.
He is credited with the discovery of the
neutron.
after Chadwick
After neutrons were discovered, isotopes of
various elements were discovered.
Neils Bohr
Bohr &
Einstein
Bohr continued with
energy calculations
and he further
developed the
planetary motion
model to include
neutrons, and
specific energies of
electrons in a certain
path.
By no means have we finished our story. We
come revisit atomic history in a little bit to learn
more about what other theories have
developed and find out where we are now.