Transcript (Atomic Theory Day 1).

Catalyst – February
•
•
3
2
– 6, 2010
HOMEWORK OUT PLEASE!
Write a sentence describing what a
theory is.
Why weren’t cell phones invented when
regular phones were?
Today’s Agenda
Catalyst
 Unit 1 Tracking
 Atomic Theory Part 1
 Exit Question

Today’s Objectives
SWBAT describe the evolution of the
atomic theory from 420 B.C. to 1898.
 SWBAT defend a conclusion using
research as evidence.

What is an atom?
Key Point #1: An
atom is the
smallest part of an
element that
retains (keeps) the
properties of the
element
Well then, what is an element?
Key Point #2: An element is a pure
substance that cannot be broken down
into simpler substances by physical or
chemical means
NOT THIS KIND OF ELEMENT
Well then, what is an element?
Key Point #2: An element is a pure
substance that cannot be broken down
into simpler substances by physical or
chemical means
NOT THIS KIND OF ELEMENT
Well then, what is an element?
THESE
KINDS OF
ELEMENTS
Why is the atom so important?
The atom is the building block
of all matter!
Without atoms, our universe
would no exist!
Essential Questions for Unit 2
1)
2)
3)
4)
What are the most important contributions
to the development of atomic theory?
What makes one atom different from
another? How are atoms similar?
Why is it so important to understand how
the periodic table is organized?
What secrets can we uncover about the
elements using the periodic table?
Atomic Theory

Atomic theory is the theory we will focus on in
Chemistry
 It
is theory of the nature of matter (stuff)
 Tells us that all matter is composed of atoms
 The specifics of the theory have change a lot
Why is atomic theory considered a theory instead
of a fact?
 Why do you think the theory
changed throughout history?

Major Playas of Atomic Theory
Democritus (460-370 B.C.)
John Dalton (1808)
J.J. Thomson (1897)
Ernest Rutherford (1909)
Niels Bohr (1913)
Schrodinger (1924)
In the beginning…

Around 420 B.C. Democritus, a Greek
philosopher, was the first to think of the
idea of atoms
A

philosopher is a thinker
Around the same time Aristotle, a more
famous philosopher, proposed a
different idea.
What were Democritus’ ideas?
•Matter is composed of tiny
particles called atomos
•Different kinds of particles
have different sizes and shapes
•Particles move through empty
space
In the beginning…

Aristotle gave us this quote…
“We are what we repeatedly
do. Excellence, therefore, is
not an act but a habit.”

Among other things…
 He challenged the ideas of
Democritus
 He did not think the “nothingness” of
empty space could exist
Questions to Ponder…

Why was Democritus’ idea not a
theory?
Then came along…


In 1808, John Dalton came up with the first atomic
theory that was based on scientific research.
It stated:
1) All matter is made of atoms.
 2) Atoms are indivisible and indestructible.
 3) All atoms of a given element are identical in mass and
properties
 4) Compounds are formed by a combination of two or more
different kinds of atoms.
 5) A chemical reaction is a rearrangement of atoms.

What were Dalton’s conclusions?
Atoms are hard,
round, solid balls.
They are similar to
marbles.
Questions to Ponder…


Why would people believe John Dalton
and not Democritus?
What makes John Dalton’s ideas about
the atom a theory and Democritus’ ideas
a thought?
But Dalton Was Wrong! (kind of)

In 1897, J.J. Thompson performed the
Cathode Ray Experiment
Shot
a beam of electrons from one end of
a tube to the other
Thompson’s Hypothesis

Thompson hypothesized that:
The
beam went from the negative side to
the positive side.
Since
opposites attract the particles must
be negative
Thompson’s Conclusions

Atoms have parts of them that are negatively
charged
 Scientists
knew from before that atoms are
neutral (no charge)

Question to Ponder…
What
other piece of information can
scientists infer about atoms based on the
above information?
The Old Theory

Recall Part 2 of John Dalton’s Atomic
Theory
2)

Atoms are indivisible and indestructible.
Question to Ponder…
How did J.J. Thompson’s Experiment
affect this part of the Atomic Theory?
Theories and Evidence

When evidence is found that does not
support a theory, the theory has to be
modified to include the new evidence
A
new theory must be made
J.J. Thompson’s New Model

The new model was called the Plum Pudding Model
 Plum
pudding is like raisin oatmeal
 The negative particles floated in a sea of positive
charge like raisins in oatmeal
Dalton’s Model
Plum
Pudding
Model
Thomson is so hood…
Now I have finished
my model! It looks
like Plum Pudding!
Classwork/Homework

Classwork: Read and create a 1 page outline for
the following pages in your textbook:
 65-67
(Democritus and Dalton)
 70-71 (JJ Thompson)

Homework:
 Answer
 Look
all the questions on the half sheet of paper
in your notes and your book for clues
Exit Question
1.
2.
Why was Dalton’s theory of the
atom more believable than
Democritus’?
What did Thomson discover to
dramatically change the theory of
the atom?