8th Grade Science
© Fall 2005, Pflugerville ISD, 8th Grade
8th Grade Science
PISD PowerPoint Lessons
Developed By
Ryan Gross, Park Crest Middle School
Edited By
Kenn Heydrick, Coordinator of Science & Health
© Fall 2005, Pflugerville ISD, 8th Grade
Chapter 2- Introduction to Atoms
Section 1:
Development of the Atomic
Theory
Section 2:
The Atom
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
What Do You Think?
Imagine that you have cut a
penny in half. Then, you take
one piece and half it again. Will
this continue forever, or will you
come to a point where no more
cutting is possible?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Democritus was a
Greek philosopher
who theorized that
all matter was made
of invisible particles
called atoms.
Democritus of Abdera,
about 460-370 BCE
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
His views
contrasted those of
Aristotle, who
believed in the four
elements; earth,
water, air, fire.
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Most of our
knowledge of
Democritus comes
from negative
remarks about him
in others’ writings.
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
John Dalton 1766-1844
© Fall 2005, Pflugerville ISD, 8th Grade
Dalton, a British
chemist and
teacher, did studies
and experiments in
weather,
colorblindness, and
gases.
Unit A : Chapter 2
Development of the Atomic Theory
He noticed that
elements combine in
specific proportions to
form compounds, and
theorized that their
atoms combine at the
same proportions
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Thomson’s
experiments using
a cathode-ray tube
showed that
smaller particles
make up atoms
Joseph John
“J.J.” Thomson
1856-1940
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Thomson
received the
Nobel Prize in
physics in 1906
for his discovery
of the electron.
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Rutherford, a former
student of Thomson’s
from New Zealand, tested
his teacher’s theories in
his Gold Foil Experiment.
Ernest Rutherford
1871- 1937
© Fall 2005, Pflugerville ISD, 8th Grade
•He expected his alpha
particles to go straight
through the foil, and
most of them did.
Unit A : Chapter 2
Development of the Atomic Theory
•But some of the
particles were
deflected or bounced
straight back!
Rutherford’s Gold Foil
Experiment
© Fall 2005, Pflugerville ISD, 8th Grade
•This showed that a
nucleus with a
positive charge
makes up the center
of an atom.
Unit A : Chapter 2
Development of the Atomic Theory
Bohr, a Danish
scientist who worked
with Rutherford,
described the motion
of electrons around
the nucleus.
Niels Bohr 1885-1962
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Bohr’s Atomic Model
© Fall 2005, Pflugerville ISD, 8th Grade
Bohr said that
electrons orbit
the nucleus at
specific energy
levels, and can
move from one
level to another.
Unit A : Chapter 2
Development of the Atomic Theory
To do this, Bohr
said, the
electrons must
absorb or
release energy,
often in the form
of light.
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
Erwin Schrödinger and
Werner Heisenberg’s
work with the
uncertainty principle
explained that
electrons do not travel
in orbits.
In fact, the exact path
of a moving electron
Schrödinger & Heisenberg cannot be predicted.
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Development of the Atomic Theory
The current atomic
theory states that
there are regions
inside an atom
where electrons are
likely to be found.
Electron Cloud Model
© Fall 2005, Pflugerville ISD, 8th Grade
These regions are
called electron
clouds.
Unit A : Chapter 2
The Atom
What Do You Think?
What is the smallest
thing you have ever
seen? How does it
compare to the size of an
atom?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Parts of the Atom
Nucleus
The nucleus is the small,
dense, positively charged
center of the atom.
Protons are positively
charged particles in the
nucleus
Neutrons are particles in
the nucleus that have no
charge
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Parts of the Atom
The current atomic
theory states that
there are regions
inside an atom
where electrons are
likely to be found.
Electron Cloud Model
© Fall 2005, Pflugerville ISD, 8th Grade
These regions are
called electron
clouds.
Unit A : Chapter 2
The Atom
What Do You Think?
What are some differences you
use to tell one of your
classmates from another?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Atomic Number- the Number of
Protons
The Helium atom
has two protons
in its nucleus.
Helium Atom
© Fall 2005, Pflugerville ISD, 8th Grade
•This means that
it has the atomic
number 2.
Unit A : Chapter 2
Atomic Number- the Number of
Protons
The Lithium atom
has three protons
in its nucleus.
Lithium Atom
© Fall 2005, Pflugerville ISD, 8th Grade
•This means that
it has the atomic
number 3.
Unit A : Chapter 2
Atomic Mass Number- Protons plus
Neutrons
The Helium atom
has two protons
and two neutrons
in its nucleus.
Helium Atom
© Fall 2005, Pflugerville ISD, 8th Grade
•This means that
it has the atomic
mass number 4.
Unit A : Chapter 2
Atomic Mass Number- Protons plus
Neutrons
The Lithium atom
has three protons
and four neutrons
in its nucleus.
Lithium Atom
© Fall 2005, Pflugerville ISD, 8th Grade
•This means that it
has the atomic
mass number 7.
Unit A : Chapter 2
Atomic Mass Number- Isotopes
Isotopes of Hydrogen
© Fall 2005, Pflugerville ISD, 8th Grade
Notice that these isotopes
of hydrogen have the
same number of protons,
but different numbers of
neutrons.
Unit A : Chapter 2
Atomic Mass Number- Isotopes
These isotopes are also known as
Hydrogen-1, Hydrogen-2, and Hydrogen-3
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Let’s Review!
-1-
In the history of
science, what are some
ways scientists have
described the atom?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Let’s Review!
-2 -
What are the parts of an
atom, and how is an
atom structured?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Let’s Review!
-3 -
What is the atomic
number of an atom? How
is this different from the
atomic mass number?
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2
Atomic Theory
•http://education.jlab.org/qa/history_02.html
•http://www.chemheritage.org/EducationalServices/c
hemach/ppt/jd.html
•http://www.aip.org/history/electron/jjhome.htm
•http://www.chemheritage.org/EducationalServices/c
hemach/ans/er.html
•http://nobelprize.org/physics/laureates/1922/bohrbio.html
© Fall 2005, Pflugerville ISD, 8th Grade
Unit A : Chapter 2