Mr. Davis Baltimore Poly
1.
2.
Are electrons more likely to fill the highest
or lowest available energy states?
What is a valence electron?

What is the potential energy of an object at
height ‘H’
Potential Energy = mgh

Is the ball’s potential energy increasing or
decreasing?
Decreasing!!!

What type of energy transfer is this?
Potential Energy to Kinetic Energy

In your Phet Lab, what happened when the
electron was hit by a photon?
1) The electron jumped to a higher energy
state
2) Soon after the electron fell back down to the
ground state.
3) The electron emits a photon
1) The electron jumped to a higher energy
state
2) Soon after the electron fell back down to the
ground state.
3) The electron emits a photon

In your Phet Lab, did the electron spend more
time in the ground state or a higher state?
The Ground State.

Electrons work in the same way as the
ball does. They tend to have a lower
potential energy.
 The
lowest band of allowed
energy states of an atom.
 Band:
a range of states.


Valence electrons reside in the
Valence Band.
If given enough energy,
electrons can escape
the Valence Band.
Conduction Band: Upper band of
allowed energy states
Electrons are free to move
around the crystal/lattice and have
very high energies.

Is the Conduction band more likely to have
more or fewer electrons than the Valence
band?
MUCH LESS
Conduction Electrons must have high energies

 Often
Empty
◦ Electrons need energy to get to this
band
Electrons
only last in this band for
fractions of a second
◦Drop back down to the Valence Band

Are there more electrons in the Valence band
or the Conduction Band?
Valence Band!!!!
Electrons in the Conduction Band quickly fall
back down to the Valence Band


The energy needed to break electron
bonds in an atom
◦ Releases the electron from its atom

Electron leaves the Valence Band and
“jumps” to the conduction band.
 What
are different ways we can
energize atoms?
 Light
Increases the energy
 What
are different ways we can
energize atoms?
 Heat
Increases the energy


What is generated when Electrons move
through a material?
A Current is caused by moving electrons
 What
A
is a conductor?
material that permits the
flow of electrons
 What
A
is a Insulator?
material whose electrons do
not flow freely

No band gap
◦ The valence band overlaps the conduction band

What is an example of a Conductor you use
Used in electronics
to facilitate electron
everyday?
flow.
 Power Lines!!!



Small Band Gap
Used in electronics
to transmit electrons

Thermal energy can bridge the gap for
a small fraction of electrons


At ordinary temperatures,
no electrons can “jump” to
the conduction band
Prevent the flow of
electrons


Match the description on your desks
to one of the three material types we
learned yesterday.
Afterwards we will go over it as a
class.


Describe how the band gap of the
materials we learned about today,
Insulators, Semi-conductors, and
Conductors effects the flow of
electrons through the material.
Periods 4 and 7


Match the description on your desks
to one of the three material types we
learned yesterday.
Afterwards we will go over it as a
class.


What is generated when Electrons move
through a material?
A Current is caused by moving electrons


Describe how electrons move through an
Insulator, if they move at all.
In an Insulator current cannot flow freely.


Describe how electrons move through an
Conductor, if they move at all.
In a Conductor electrons can flow freely
through the material.

An Electron in the Conduction Band
that moves through the material

Not attached to an atom

What is Avogadro’s Number?
( N A )  6.02 x 10 atoms / mol
23

The number of atoms in a mole of a
substance
Number of
Free electrons =

free e
1
(
)( N A )( )( m)
atom
M
Free electrons per atom
M = Molar Mass
m = mass of the substance


Cadmium has 2 free electrons per atom and a
Molar Mass of 112.40 g/mol. How many free
electrons are there in 1g of cadmium?
What is our unknown?
◦ The Number of Free Electrons


Cadmium has 2 free electrons per atom and a
Molar Mass of 112.40 g/mol. How many free
electrons are there in 1g of cadmium?
What are our knowns?
◦ Free Electrons per Atom = 2
◦ Molar Mass = 112.40 g/mol.
◦ Mass = 1g


Cadmium has 2 free electrons per atom and a
Molar Mass of 112.40 g/mol. How many free
electrons are there in 1g of cadmium?
What is our equation?

free e
1
Num of Free Electrons  (
)( N A )( )( m)
atom
M
Number of
Free electrons =
V = Volume

Free e
(
)V
3
cm
What is the unit for volume?
cm3 or a distance cubed
Number of
Free electrons =
Number of
Free electrons =
Free e 
3
(
)(
cm
)
3
cm
Free e



# of free e
Free e
1

(
)(
N
)(
)(

)
A
3
cm
atom
M
ρ =Density
# of atoms
1

(
N
)(
)(

)
A
3
cm
M
ρ =Density
1
# of atoms  ( N A )( )( m)
M
atoms
# of atoms  (
)(V )
3
cm


That was a lot of equations!!!
How will you know when to use which
equation?


Identify your Unknown

Determine your Givens
When solving a problem,
WRITE THESE THINGS DOWN

Silver, with a density of 10.5 g/cm3 and an
atomic mass (molar mass) of 107.87 g/mol,
has one free electron per atom. How many
free electrons are there in each cubic
centimeter of silver?
 Spend
the rest of class
working on “Solid-State
Electronics”.
 It is due Monday.
 You must complete three
problems by the end of class.
1.
At 200.0K, silicon has 1.89 x 105
free electrons/cm3, a density of
2.329 g/cm3, and an atomic mass of
28.09 g/mol. How many free
electrons are there per atom at this
temperature?
How does doping
work in sports?
We insert a foreign
substance into our
bodies to improve
performance


Not in sports but in Semiconductors!
Semiconductor: conducts electricity under some
conditions but not others

Doping- Inserting a different element into a
material to change its properties

Dopant: a trace impurity element that is
inserted into a substance

Inserted at LOW Concentrations

Alters the electrical properties


Goal is to increase the number of free charge
carriers (moving electrons) .
Add material that takes away our free
electrons, causing them to move

Hole: vacancy left behind by the electron


Our element wants to have three electrons
per table.
Now we want to element p-type doping. Do
we want to add a table with more or less
electrons?

Less

Want to create an abundance of holes to
increase electron flow.

What is generated when electrons are
moving?

A Current!!!!


Add material that provides us extra free
electrons
Creates an excess of negative electron charge
carriers

These Extra Electrons allow for the flow of
Current


Our element wants to have three electrons
per table.
Now we want to element n-type doping. Do
we want to add a table with more or less
electrons?

More

Device that conducts electricity in only one
direction

Used to:
◦ Tune Radios and TV receivers
◦ Generate Radio Frequencies

A semiconductor used to amplify and switch
electronic signals

https://www.youtube.com/watch?v=IcrBqCFLHIY

Watch a quick video on transistors

Shows us how this works for all of our
technology we use everyday.
 Spend
the rest of class
working on “Solid-State
Electronics”.
 It is due Monday.
 Exit
Ticket at the end of class.

Based on what you saw in the video and in
class today, Describe how the two different
types of semiconductors allow for the
movement of electrons to generate a current.
1.
A metal has 1.92 x 1023 free
electrons per cubic centimeter. If its
atomic mass is 26.982 g/mol and it
has three free electrons per atom,
what is its density?
Keep your Do Nows
Pass in your Homework
 Today
we will be headed to the
lab, Room 127
 The
lab is due tomorrow so
work diligently.
 At
the end of the lab there is a
chance to earn bonus points and
a bonus assignment.
How many atoms of germanium are
there in one cubic centimeter of
germanium? The density of germanium
is 5.35 g/cm3 and its molar mass is
72.64g/mol.
1)
2)
What do the “N” and “P” in the different
types of dopants stand for?
Pass in your lab

Today:
◦ Quiz Review, Key at the front and back of
the class

Tomorrow:
◦ Tic-Tac-Toe Review
◦ You pick which activities you want to do.

By the end of class today you need to have
completed:
◦ 8 Problems of your Quiz Review
◦ I will come around and stamp this for a grade.
◦ If you finish the Quiz Review you will be given tomorrow’s
Review activity.

Group Exit Ticket at the end of class

What is at least one thing you would
like to review as a class tomorrow
before the Quiz on Thursday?
1)
Cadmium has 2 free electrons per
atom. How many free electrons are
there in three cubic centimeters of
cadmium?
Element
Density (g/cm3)
Atomic mass (g/mol)
Copper
8.94
63.54
Gallium
5.91
69.72
Cadmium
8.65
112.40
Germanium
5.323
72.59
Zinc
7.14
65.37
Indium
7.31
114.82
Aluminum
2.70
26.98
Silicon
2.3290
28.09
Sodium
0.968
22.99

You can pick any three boxes that give you
Tic-Tac-Toe
◦ Two of the boxes require materials from
the classroom
 The Challenge Problems
 Text Book Problems
◦ If you want to work on those boxes, materials are
up front.

By the end of class today you need to have
completed:
◦ Two Boxes on your Tic-Tac-Toe Review
◦ I will come around and stamp this for a grade.

Each extra box on the Tic-Tac-Toe Review you
complete is an extra point on your quiz
◦ (Up to 6% Extra Credit to your Quiz)

EXTRA SLIDES AFTER THIS
Variety of ways to build molecules:

Ranges from Simple lattice to Complex shapes