Mr. Davis Baltimore Poly. 1. Are electrons more likely to fill the highest or lowest available energy states? 2. What is a valence electron?

Solid StateMr. Davis Baltimore Poly

1. Are electrons more likely to fill the highest or lowest available energy states?

2. What is a valence electron?

Do Now (4/2/14) (3 minutes)

What is the potential energy of an object at height ‘H’

Potential Energy = mgh

Energy Levels

Is the ball’s potential energy increasing or decreasing?

Energy Levels

Decreasing!!!

What type of energy transfer is this?

Energy Levels

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

Electron Energy Levels

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.

Energy

The lowest band of allowed energy states of an atom.

Band: a range of states.

Valence Band:

Valence electrons reside in the Valence Band.

If given enough energy, electrons can escape the Valence Band.

Valence Band

Conduction Band: Upper band of allowed energy states

Electrons are free to move around the crystal/lattice and have very high energies.

Conduction Band

Is the Conduction band more likely to have more or fewer electrons than the Valence

band?

MUCH LESSConduction Electrons must have high

energies

Conduction Band (30 seconds)

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

Conduction 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

Conduction Band (30 seconds)

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.

Band Gap Energy

What are different ways we can energize atoms?

Light Increases the energy

How do we energize atoms?

What are different ways we can energize atoms?

Heat Increases the energy

How do we energize atoms?

Heat

Light

What is generated when Electrons move through a material?

A Current is caused by moving electrons

Moving Electrons

What is a conductor?

A material that permits the flow of electrons

Conductors

What is a Insulator?

A material whose electrons do not flow freely

Insulator

No band gap ◦ The valence band overlaps the conduction band

Conductors

Used in electronics to facilitate electron flow.

Conductors What is an example of a Conductor you use

everyday? Power Lines!!!

Small Band Gap

Used in electronicsto transmit electrons

Semi Conductors

Thermal energy can bridge the gap for a small fraction of electrons

Semi Conductors

At ordinary temperatures, no electrons can “jump” to the conduction band

Prevent the flow of electrons

Insulators

All Three Materials

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.

Classwork (3 minutes)

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

Exit Ticket (3 minutes)

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

Moving Electrons

Describe how electrons move through an Insulator, if they move at all.

In an Insulator current cannot flow freely.

Moving Charges

Describe how electrons move through an Conductor, if they move at all.

In a Conductor electrons can flow freely through the material.

Moving Charges

An Electron in the Conduction Band that moves through the

material

Not attached to an atom

Free Electrons

What is Avogadro’s Number?

The number of atoms in a mole of a substance

Avogadro’s Number

molatomsxN A /1002.6)( 23

Free Electrons (1)

))(1

)()(( mM

Natom

efreeA

Number of Free electrons =

Free electrons per atomM = Molar Massm = 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

Guided Practice (2 minutes)


What are our knowns?

◦ Free Electrons per Atom = 2◦ Molar Mass = 112.40 g/mol.◦ Mass = 1g



What is our equation?


))(1

)()(( mM

Natom

efreeElectronsFreeofNum A

Free Electrons (2)

Vcm

eFree)(

3


V = Volume

Free Electrons

What is the unit for volume?

cm3 or a distance cubed

Free Electrons (2 continued)

))(( 33

cmcm

eFree Number of Free electrons =


eFree

Free Electrons (3)

))(1

)()((#

3

MN

atom

eFree

cm

efreeofA

ρ =Density

Free Electrons (4)

))(1

)((#

3

MN

cm

atomsofA

ρ =Density

Free Electrons (5)

))(1

)((# mM

Natomsof A

Free Electrons (6)

))((#3V

cm

atomsatomsof

That was a lot of equations!!!

How will you know when to use which equation?

Free Electrons

Identify your Unknown

Determine your Givens

When solving a problem,

WRITE THESE THINGS DOWN

Free Electrons

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?

Practice (5 Minutes)

Classwork

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

Doping

Not in sports but in Semiconductors!

Semiconductor: conducts electricity under some conditions but not others

Doping

Doping- Inserting a different element into a material to change its properties

Doping

Dopant: a trace impurity element that is inserted into a substance

Inserted at LOW Concentrations

Alters the electrical properties

Dopant

Goal is to increase the number of free charge carriers (moving electrons) .

Add material that takes away our free electrons, causing them to move

P-Type Semiconductor

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

Classroom Example

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

N-Type Semiconductor

These Extra Electrons allow for the flow of Current

N-Type Semiconductor

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

Classroom Example

Device that conducts electricity in only one direction

Diodes

Used to:◦ Tune Radios and TV receivers ◦ Generate Radio Frequencies

Diodes

A semiconductor used to amplify and switch electronic signals

Transistor

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.

Video

https://www.youtube.com/watch?v=IcrBqCFLHIY

Classwork

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.

Exit Ticket (5 minutes)

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 NowsPass in your Homework


Today we will be headed to the lab, Room 127

The lab is due tomorrow so work diligently.

Lab

At the end of the lab there is a chance to earn bonus points and a bonus assignment.

Lab

1) 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.

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.

Two Day Review

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

Classwork (4/8/14)

What is at least one thing you would like to review as a class tomorrow before the Quiz on Thursday?

Group Exit Ticket (3 minutes)

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.

Tic-Tac-Toe

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)

Classwork (4/9/14)

EXTRA SLIDES AFTER THIS

Crystal Structure

Variety of ways to build molecules:

Ranges from Simple lattice to Complex shapes

Documents

Mr. Davis Baltimore Poly. 1. Are electrons more likely to fill the highest or lowest available energy states? 2. What is a valence electron?