1. Chapter 3

2. Section 1

3. Greek philosophers devised a
theory of atoms, or tiny particles.
Didn’t use experiments
Used discussion, debate and
reason - no evidence or proof.

4. All matter is made up of
elements – matter made up
of atoms of one kind.
EX: Silver – silver atoms

5. John Dalton combined the
idea of elements with the
Greek theory of the atom.
Matter is made up of atoms.
Atoms cannot be divided
into smaller pieces.

6. All atoms of an element are
exactly alike.
Different elements are made of
different atoms.

7. Dalton’s Theory was tested by
William Crooks and his cathode-
ray tube experiment.
Crooks hypothesized that the
green glow in the tube was
caused by a stream of particles.
Cathode Rays

8. Cathode Ray Tube
CRT
Used in TV and computer screens
for many years.

9. JJ Thomson discovered
negatively charged particles,
electrons, which are part of every
atom.

10. Thomson revised Dalton’s model
to include a sphere with a
positive charge & negatively
charged electrons spread evenly
within the positive charge.

12. The negatively charged electrons
and the positive charge in the
sphere neutralized each other.

13. Earnest Rutherford tested
Thomson’s model.
Rutherford and his coworkers
began an experiment to find
out if Thomson's model of the
atom was correct.

14. They wanted to see what would
happen when they fired fast
moving, positively charged bits
of matter, called alpha
particles, at a thin film of a
metal such as gold.

15. Alpha particles, which come
from unstable atoms, are
positively charged, and so they
are repelled by particles of
matter that also have a positive
charge.

16. Rutherford was certain he knew
what the results of this
experiment would be.
His prediction was that most of
the speeding alpha particles would
pass right through the foil and hit
the screen on the other side.

17. Rutherford was shocked when his
student rushed in to tell him that
some alpha particles were veering
off at large angles.

18. The positively charged alpha
particles were moving with such high
speed that it would take a large
positive charge to cause them to
bounce back.
The uniform mix of mass and
charges in Thomson's model of the
atom did not allow for this kind of
result.

19. An atomic model with a
nucleus was developed.
The positively charged proton
is located in a very small space
at the center of the atom.

20. Most of an atom is empty space
occupied by nearly massless
electrons.
Rutherford's nuclear model was
applauded as other scientists
reviewed the results of the
experiments. However, some data
didn't fit.

21. Because the atom was only
protons and electrons and
electrons are “massless” the mass
of an atom should have been
approximately equal to the mass
of its protons.

22. It isn’t.
The mass of most atoms is at least
twice as great as the mass of its
protons.
It was proposed that another
particle must be in the nucleus to
account for the extra mass.

23. Electrically neutral particles,
neutrons, are also located in the
nucleus.
The number of electrons equals
the number of protons in an atom.

24. Solar System Model

25. The electron cloud model explains
the unpredictable wave behavior
of electrons, which could be
anywhere in the area surrounding
the nucleus.
http://www.edumedia-
sciences.com/en/a66-electron-
distribution

26. Explain how the nuclear atom
differs from the uniform sphere
model of the atom. SC.A.2.3.2
In the nuclear atom, all the positive
charge & almost all of the mass are in
a tiny nucleus with electrons
occupying the space around it.
The uniform sphere model stated the
atom was the smallest type of matter
and the same throughout.

27. Determine how many electrons a
neutral atom with 49 protons
has. SC.A.2.3.2
49 electrons

28. Cathode rays are Crookes
hypothesized that the greens glow
in the tube was caused by rays.
 They this discovered cause TV and
computer have display screens.

29. Design and complete a concept
map using all the words in the
vocabulary list for this section.
Add any other terms or words that
will help create a complete
diagram of the section and the
concepts it contains.

30. Element
Atom
Nucleus
Neutrons Protons
E cloud
electron

31. In Rutherford's experiment, why
wouldn't the electrons in the
atoms of the gold foil affect the
paths of the alpha
particles? SC.A.2.3.2
Because most alpha particles
could move through the foil with
little or no interference because of
the empty space that makes up
most of atom.