This document discusses the development of atomic structure models from ancient Greek philosophers through Rutherford's experiments. It describes Dalton's atomic theory that matter is made of atoms that cannot be divided further. Rutherford discovered that alpha particles fired at a gold foil occasionally bounced off at large angles, inconsistent with Thomson's uniform sphere model. This led to Rutherford's nuclear model with a small, dense nucleus containing positive charge and most mass, surrounded by electrons in empty space. Later, neutrons were discovered in atomic nuclei.

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.