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10/27
DO NOW
Hmmm – Write down your thoughts to
these open ended questions:
1.
How can we know what's in an atom
if we can't even see one?
2.
Is there anything smaller than
protons, neutrons and electrons?
AGENDA 10/27
1.
2.
3.
4.
5.
Do Now
Go over test
HW on the website
Handouts
Begin Chapter 4 (if time)
HW: None
The Structure of the Atom
CHAPTER 4
ELEMENTS?
Early philosophers sought answers to explain the universe.
They thought: All substances were built up from only four elements — earth, air,
fire, and water. These elements were a combination of four qualities—hot, cold,
dry, and wet.
Ie: Fire was a combination of hot and dry.
Ie: Water was a combination of cold and wet.
4.1 STUDYING ATOMS



If you cut a piece of Aluminum foil in half and continue to cut the
resulting piece in half, what will happen?
Are we slicing an atom in half??
Greek Philosophers pondered this 2500 years ago.
 Democritus- believed all matter consisted of extremely small
particles that could not be divided.


He called these particles atoms
Aristotle – did not think there was a limit to the number of times
matter could be divided.

Most people believed Aristotle until the 1800s when scientists had
enough data to support Democritus
MYSTERY OF THE ATOM
Lots of people tried to figure out:
1. What the atom looked like
2. How atoms behave
DALTON’S ATOMIC THEORY
DALTON- noticed something
weird…in 1800’s

He noticed that no matter how
big or small a quantity of
something you have, the ratio of
masses of the elements in a
compound is always the same.
 Dalton
proposed a theory that all
matter is made up of
individual particles called atoms,
which cannot be divided.
The Atom
MAIN POINTS OF DALTON’S ATOMIC THEORY
1.
2.
3.
All elements are composed of atoms.
All atoms of the same element have the same
mass, which are unique from other elements.
Compounds contain more than 1 element.
Note: This isn’t news!
We already learned
these above!
MAIN POINTS OF DALTON’S
ATOMIC THEORY
4. In a compound, atoms always combine the
same way.
5. Dalton thought elements were solid spheres.
Each type of atom is represented by a tiny, solid
sphere with a different mass.
6. Eventually, scientists discovered not all of
Dalton’s theories were correct…
Note: This STILL isn’t news!
- You know this stuff.-
THOMSON’S MODEL OF THE ATOM
J.J. Thomson- 1856-1940
 Atoms
have positive and negative charges.
 Objects
with like charges repel, or push apart.
 Objects with opposite charges attract or pull together.
 Some
charged particles can flow from one location
to another (electric current)
 Thomson used an electric current to learn more
about atoms.
0
+
-
CATHODE-RAY TUBE EXPERIMENT
A cathode-ray tube is a sealed tube with a metal
disk at each end. One is positive and one is
negative.
 A glowing beam appears between the two disks.

Thomson used a sealed
tube of gas in his
experiments. When the
current was on, the disks
became charged and a
glowing beam appeared in
the tube
CATHODE RAY TUBE EXPERIMENT



Thomson discovered the beam was deflected when
additional charged plates were placed on the sides of the
tube.
Thomson concluded the beam must be negative charges.
He hypothesized the charges came from inside the atom.
Thomson’s experiments provided the first evidence that
atoms are made of even smaller particles.
The beam bent
toward a positively
charged plate placed
outside the tube
THOMSON’S MODEL
His model of the atom looked like “plum pudding”
(or chocolate chip ice cream). The pudding had
an overall positive charge and the negative
charges were randomly placed throughout.
Overall, the atom is neutral.
RUTHERFORD’S HYPOTHESIS
 1899 Ernest Rutherford
discovered Uranium emits
fast-moving particles that have
a positive charge. (He called
them alpha particles)

1909 he asked his student, Ernest Marsden, to see
what happens when the alpha particles are passed
through a thin sheet of gold.


He hypothesized most particles would travel in a straight
path from their source.
Some would be deflected slightly.
RUTHERFORD’S GOLD FOIL EXPERIMENT
RUTHERFORD’S ATOMIC THEORY


ACTUAL EXPERIMENTAL RESULTS
 More particles were deflected than he was
expecting. Some particles deflected as
much as 90º. Others bounced straight
back.
DISCOVERY OF THE NUCLEUS
 Nucleus- dense, positively charged mass
located in the center of the atom.
 Rutherford proposed a new model of the
atom.
 All of the atom’s positive charge is
concentrated in its nucleus. This
explains why alpha particles had a
greater deflection the closer they were
to the nucleus (both have positive
charges)
If the stadium were a
model for an atom, a
marble could represent
its nucleus.
EXIT TICKET
Answer these on the back of your notes packet:
1.
Who discovered that subatomic particles exist?
2.
List the atomic scientists in timeline order.
3.
Contrast Democritus’ model to Rutherford’s
model.
4.
In your own words, describe the cathode ray
tube experiment, and what it meant.
4.2 STRUCTURE OF AN ATOM
Properties of Subatomic Particles
 Protons, electrons, and neutrons are all subatomic
particles

PROTONS- Positive charge subatomic particle found in the
nucleus. They each have a charge of 1+. Each nucleus
contains at least one particle with a positive charge.
 ELECTONS- Negatively charged subatomic particle that is
found in the space outside the nucleus. Each electron
has a charge of 1-.
 NEUTRONS- Neutral subatomic particle that is found in
the nucleus of an atom. It’s mass is nearly equal to the
mass of a proton.

 In
1932 - experiment to show neutrons exist. It was similar to
Rutherford’s gold foil experiment. The neutrons showed no
deflection.
COMPARING SUBATOMIC PARTICLES

Protons, electrons and neutrons can be distinguished by
mass, charge, and location in the atom.



Protons and neutrons have equal mass.
Electrons are 1/2000 the mass of a proton.
Electrons have a charge that is equal in size to, but the opposite
of, the charge of a proton.
Neutrons have no charge.
Protons and neutrons are found in the nucleus, but electrons
are found in the space outside the nucleus.
ATOMIC NUMBER AND MASS NUMBER

Atomic number- Equal to the number of protons in an
atom of that element.
Hydrogen (H) atoms are the only atoms with 1 proton.
 Atoms of different elements have different numbers of
protons.
 Each positive charge is balanced by a negative charge.

Each element has a
different atomic number. A
The atomic number of
sulfur (S) is 16. B The
atomic number of iron (Fe)
is 26. C The atomic number
of silver (Ag) is 47.

Mass number- Sum of the protons and neutrons
in the nucleus of that atom.
#

of neutrons = mass # - atomic #
Isotopes
 Every
atom of a given element does have the same
number of protons and electrons.
 But every atom of a given element does not have the
same number of neutrons.
 Isotopes of an element have the same atomic
number but a different mass number because they
have different numbers of neutrons.

With most elements, it’s hard to notice any differences
in the physical or chemical properties of their isotopes.

Hydrogen is the exception.
Normal hydrogen (H-1) has no neutrons (most of all H)
H-2 has 1 neutron –mass has doubled.
H-3 has 2 neutrons –mass has tripled.
Heavy water is made from H-2 atoms.



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4.3 MODERN
ATOMIC THEORY

BOHR’S MODEL OF THE ATOM
 Niels
Bohr’s model did something Rutherford’s
model did not do. It focused on the electrons.
 Electrons
move with constant speed in fixed orbits
around the nucleus (like planets around the sun)
 Each electron in an atom has a specific amount of
energy.
 ENERGY LEVELS- the possible energies that electrons in
an atom can have.
UNDERSTANDING ENERGY LEVELS

Picture energy levels as steps in a staircase.


You can go up or down the steps, but only in whole-step
increments. You cannot stand between steps on a
staircase. Electrons cannot exist between energy
levels.
An electron in an atom can move from one energy
level to another when the atom gains or loses
energy.
The size of the jump determines the amount of energy
gained or lost.
 Energy released as the electron jumps back down to its
lower energy levels is often given off in the form of
visible light.
 Different elements emit different colors of light.

ELECTRON CLOUD MODEL
Bohr was incorrect in assuming
electrons moved like planets in a
solar system. They are actually
less predictable.
 ELETRON CLOUD- a visual model of the most likely
locations for electrons in an atom. The cloud is
denser at the locations where the probability of
finding an electron is higher.
 Scientists use the electron cloud model to
describe the possible locations of electrons
around the nucleus.

ELECTRON CLOUD ANALOGY
When the propeller of an airplane is at rest, you can see the
locations of the blades. When the propeller is moving, you see
only a blur that is similar to a drawing of an electron cloud
ATOMIC ORBITALS



Orbital- is a region of space around the nucleus where an
electron is likely to be found.
An electron cloud is a good approximation of how electrons
behave in their orbitals
The level in which an electron has the least energy—the
lowest energy level—has only one orbital. Higher energy
levels have more than one orbital
ELECTRON CONFIGURATIONS

Electron Configuration is the arrangement of
electrons in the orbitals of an atom.
The most stable electron configuration is the one in
which the electrons are in orbitals with the lowest
possible energies.
 When all the electrons in an atom have the lowest
possible energies, the atom is said to be in its ground
state
 If one electron can move to an orbital with a higher
energy it is referred to as an excited state.
 An excited state is less stable than the ground state.

RULES FOR DRAWING BOHR MODELS
Electrons like to be:
1. In a pair, if possible
2. In a closed orbital of 8 (or 2 in orbital 1)
**2-8-8-8 Rule! **
3. Drawn Top/Bottom in Orbital 1
4. Drawn Top/Right/Bottom/Left until all
electrons are placed in pairs
LEARNING OBJECTIVES
Students will understand:
-
- That many theories of the atom failed, and
were corrected over hundreds of years
-
- The important differences in atomic theories,
and how to draw the models
11/4 AGENDA
1.
2.
Do Now
Begin Chapter 4: Atomic
Structure
- History of Atomic Discovery
3.
4.
5.
“Draw the Atom” Timeline
Exit Ticket
No HW
11/10
DO NOW
Give a written explanation, in your own words:
1.
2.
Describe, and then give the importance of the
cathode ray tube experiment
Describe, and then give the importance of the
gold foil experiment.
Then, share with your partner. 1 partner explain
#1, and the other partner explain #2
11/10 AGENDA
1.
2.
Do Now
Chapt 4: Atomic Structure
- Mass, Particles, and Isotopes
3.
4.
Exit Ticket - Isotopes
HW – 4.1 and 4.2
11/11 HAPPY VETERAN'S DAY - THANK VETERANS TODAY
Neutron - n
Proton – p+
Electron – e-
11/11
AGENDA