Transcript WAY BACK WEDNESDAY! February 144/48 - stroh

WAY BACK WEDNESDAY!
February 144/48 , 2.010 x 103
DINOSAUR HOMEWORK FROM MONDAY PLEASE!

A 500 kilogram man steps on a scale
wanting to see if his new diet will make
him lose mass (weight).
1. Describe a set of three measurements
that would be PRECISE but not
ACCURATE.
2. Convert his mass to milligrams.
3. What is the IV? DV? 2 Constants?
Today’s Agenda
Catalyst
 Unit 1 Test Tracking
 Quick Review of the Old Guys
 Story heats up- the final 3 playas
 Unit Test Practice!
 Exit Question

Today’s Objectives

SWBAT describe the
development of the modern
atom.
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
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)
Democritus
(460-370 B.C.)

Experiment: Observations and inferences
 No
REAL experiment…just IDEAS
Where: Greece
 When: 420 B.C.
 First “theory” of the atom

Page 88
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…

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.
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?
John Dalton (1766-1844)
•Experiment:
Careful chemical
measurements
•Where: England
•When: 1808
Page 90
Then came along…


In 1808, John Dalton came up with the first atomic
theory that was based on scientific research.
It stated:
1.
2.
3.
4.
5.
All matter is made of atoms.
Atoms are indivisible and indestructible.
All atoms of a given element are identical in mass and
properties
Compounds are formed by a combination of two or more
different kinds of atoms.
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
J. J. Thomson (1856-1940)
•Experiment: Cathode ray
tube
•When: 1897
•Where: England
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 was pretty hungry when…
Now I have finished
my model! It looks
like Plum Pudding!
Quick Review

Democritus – 200 B.C. – First to think atoms exist


Dalton – 1808 – First atomic Theory


Not a theory. No Proof. Overshadowed by Aristotle
Based on scientific evidence
JJ Thompson – 1898 – Cathode Ray Experiment

Showed presence of small negative parts of atoms

These parts are called electrons
Implied presence of positive parts
 Showed atoms are NOT indivisible
 Developed Plum-Pudding Model

But Thompson was wrong too!

In 1909, Ernest Rutherford performed the Gold Foil
Experiment
 Shot
alpha particles (positively charged and gigantic)
at a very thin piece of gold foil
What should have happened…


Alpha particles are 8000 times the size of an
electron.
If the plum-pudding model were true all of the
positively charged alpha particles should have
gone straight through the foil.
What Actually Happened…

Almost all, of the alpha particles went straight
through, some were deflected a little, some were
deflected a lot.
1
in 8000 of the particles was deflected
?
More History
Ernie’s (Rutherford) Big Adventure
Thin Sheet of Gold
Atoms
Can YOU figure it out? (3 min)
Pretend you are Rutherford (during
simulation)
 As Rutherford, what conclusion would you
make based on the data from the Gold
Foil Experiment?

Hint: Positive repels
positive, negative
repels negative
=
Simulation
http://phet.colorado.edu/simulations/si
ms.php?sim=Rutherford_Scattering
-
++
++
-
-
What were Rutherford’s conclusions?
•Discovered the nucleus, a
concentrated mass with
positive protons!
•Nucleus is in the center of
the atom
•The atom is mostly empty
space
Rutherford’s Conclusion

Atoms are made of mostly
EMPTY SPACE!
 Actually,
the ratio of the size
of the nucleus to the
diameter of the orbits of
electrons can be compared
with placing a marble in the
middle of a football
stadium!
Relative Size of the Nucleus to the Atom
Empty Space Continued

“Neutrons and protons occupy the atom's
nucleus. The nucleus of an atom is tiny -- only
one-millionth of a billionth of the full volume
of the atom -- but fantastically dense, since it
contains virtually all the atom's mass. As
Cropper has put it, if an atom were
expanded to the size of a cathedral, the
nucleus would be only about the size of a fly
-- but a fly many times heavier than the
cathedral.” -A Short History of Nearly
Everything by Bill Bryson
That was intense…

Question to ponder:
But thinking logically, what do
you think would happen if there
were just electrons (-) hanging
around the nucleus (+)?
Niels Bohr (1913)


Rutherford is a
jerk! Electrons
orbit the nucleus
at specific
distances!
Bohr looked at how excited electrons gave off light
and figured out it happened in a SPECIFIC
PATTERN!
Through lots of math, he figured out that
ELECTRONS ONLY EXIST AT CERTAIN DISTANCES
FROM THE NUCLEUS!
Not BOHR-ING
AT ALL!!!
But They Knew This Wasn’t Right
There were other emission line spectra for
larger atoms that did not fit the Bohr
Model…
 So in 1924 Erwin Schrödinger added a new
detail

 Think
of the electrons as waves instead of
particles

Now the model included all the evidence
But there was still one problem
Since the electrons acted like waves, you would
never be able to tell where an electron is
 So instead of orbits, they created orbitals

 Orbitals
are like rooms that electrons are probably
in at a given moment

This final Model is called the WaveMechanical Model
 Or
the Quantum Model
Hooray!
Gallery-walk-it-out…


For this you will consolidate into 6 groups!
Each group is going to summarize 4 things
about one of the atomic theory playas.
1.
2.
3.
4.
Who did it and when?
What evidence did they have to back up their
claims?
A picture of their model.
The biggest idea to come out of their model of
the atom.
Gallery walk






You will have 2 minutes to gather information at each
station.
As noted on the sheet, you will answer:
Who created the theory/model? When?
What evidence was there to support the theory or model?
What evidence eventually proved the theory/model wrong
or caused modifications in the theory/model? (Include the
name and conclusions of the experiment)
How did the evidence above affect the theory or model?
Exit Question
1.
2.
3.
4.
How did Thomson change the theory of
Dalton?
How did Rutherford change the theory
of Thomson?
How did Neils Bohr change the theory
of his predecessor?
Why is science called the “selfcorrecting machine”?