Transcript Atomic Theory Part One

HE ATOM
T
The smallest part of an
element that has
properties of that
element.
In 1981, a type of microscope called a scanning tunneling
microscope (STM) was developed.
Photo courtesy National Institute of Standards and
Technology (NIST)
<http://www.howstuffworks.com/framed.ht m?parent=at
om.htm&url=http://nist.gov>
STM image of a single zigzag chain of cesium atoms (red) on a galliumarsenside surface (blue)
nanotechweb.org/article s/ne
ws/3/9/8/1/niststm1
MODEL
A way scientists explain
something unknown by
relating it to something that
can be seen or understood.
What are some reasons scientists use models?
You have certainly had experience with models
in science in your past. Name one of the
models you have used in science class.
Why is our current understanding of the atom still
considered a model or a theory?
Model of an
atom.
Empedocles (49- 432 BC) argued that all matter was composed of four
elements: fire, air, water, and earth. The ratio of these four elements
affected the properties of the matter.
Atomic Model Timeline
Democritus
2500 years ago
First idea of an atom
"atomos" (invisible)
Democritus
He suggested that atomos were eternal and
could not be destroyed.
Democritus theorized that atomos were
specific to the material that they made up,
meaning that the atomos of stone were
unique to stone and different from the
atomos of other materials, such as fur.
This was a remarkable theory that
attempted to explain the whole physical
world in terms of a small number of ideas.
Alchemy
Middle Ages, 1200-1600
Goal was to change cheap elements into gold
Philosopher’s Stone
The philosophers' stone is a legendary alchemical
substance, said to be capable of turning base metals,
especially lead, into gold; it was also sometimes believed
to be an elixir of life, useful for rejuvenation and possibly
for achieving immortality .
The Scientific Revolution
1600-1700’s
Copernicus-the Sun is the
center of the Solar System.
Copernicus
Galileo-advanced
telescopes &
experimental
physics
NewtonLaws of Motion &
Gravity
John Dalton
early 1800’s
“Father of the
Atomic Theory”
John Dalton
School Teacher from England
19th Century (1807)
He combined the idea of elements with the
Greek theory of atoms.
Dalton’s Atomic Theory
All matter is made of atoms
Atoms can’t be created or destroyed
All atoms of one element are the same
Atoms of different elements can combine to form new substances
John
Dalton pictured the atom as a hard sphere with the same
makeup throughout the entire atom.
William Crookes
English Scientist 1870's
Tested Dalton's theory of the atom.
Experimented with an airless glass tube with two
metal pieces hooked to a battery.
Cathode ray tube + CRT
Same type of mechanism found in tv's and computer monitors
Saw a "beam" of something from the negatively charged cathode to the
positively charged anode.
The beam looked like a grennish-yellowish light, but Crookes said it was a
beam of particles.
He couldn't prove it!!! (bummmer!)
J. J. Thomson
1897 English physicist
Worked on Crooke's experiments. Use a magnet
next to the glass tube.
Proved that the beam was not light...Light can not
be bent with a magnet.
The beam bent towards the magnet.....Opposite
charges attract.
Knew that the particles were negatively charged.
HOW?
Named the negatively charged particles
ELECTRONS.
"Plum Pudding Model of the Atom"
J J Thomson's model of the atom.
Science Work for Dec 1 ......
Your assignment is to begin filling out the Study Guide from your reading the Atomic
Theory Handout from the science site.
Read the material again if needed. Write out rough draft paragraphs of John Dalton,
William Crookes, and JJ Thomson's work on the atom and atomic theory.
Use your flash cards
Element Test is Monday, Dec 14th!!