The Bohr Model

Do Now (3/24/14) (5 Minutes) If you haven’t already Pass in Last week’s Do

Now What are some scientific examples of concepts humanity or yourself believed in

the past but we now think differently?

Myths Earth is flat and the center of universe

The Earth is 6000 years old Heavier Objects Fall Faster than Smaller Objects

Washing your hands before surgery Atoms are the smallest possible particles

History of the Atom

Notesheet Writing down notes helps you remember

material before you even start studying.

What should I write down? What the professor thinks is important. Repetition/Emphasis

Don’t copy down everything on the board!!!!

What do we know about the ATOM? Talk with your table for 1 minute about what

you already know about the atom. I will call on three random people in the class

to see what you discussed.

How big is it? What is an atom made of? What does it look like?

Dalton 1803 John Dalton an "atomic theory" with

spherical solid atoms

1) All elements are made up

of tiny spherical

particles called atoms

2) Atoms can not be

created or destroyed

JJ. Thompson 1904 JJ. Thompson Plum Pudding model

Negative Electrons are the

Plums

Positive Pudding makes up the

rest of the space

Quick, Discuss with your Elbow Partner

What are the three major particles that make up atoms?

Which particle has a positive charge? Proton

Which particle has a negative charge?Electron

Which particle has a neutral charge?Neutron

Ernest Rutherford 1911  Ernest Rutherford Nucleus of an atom was:

very dense, very small positively charged. Electrons were located

outside the nucleus. 

What is in-between the Nucleus and the Electrons?

Empty Space!!!

View of atomic Structure in early 1900’s

+Electronorbit

electrons traveled around the nucleus in orbits, like the planets

Classical (before 1900) physics could not explain why electrons don’t fall into the nucleus

Video - How did J.J. Thomson describe the atom?

Plum Pudding Model

- What model did Rutherford use to describe the atom? A Nucleus with electrons around the outside

- Why did the scientists have to adjust their model of the atom? Experimental data.

Classwork Spend the rest of class finishing the

video questions and the exit ticket.

Notesheet

Why should you write notes? Writing down notes helps you

remember material before you even start studying.

Notesheet

What should I write down? What the professor thinks is important. Repetition/Emphasis

Don’t copy down everything on the board!!!!

Do Now (3/25/14) (5 minutes):

1.Describe the structure of an atom.

2.Draw a picture of an atom.

1. (I will need three volunteers to draw their atom)

Rutherford’s Model

+Electronorbit

How did Rutherford describe the motion of electrons around the nucleus?

Classical (before 1900) physics could not explain why electrons don’t fall into the nucleus

Rutherford Model This is a big flaw in Rutherford’s

model.

They didn’t know why electrons don’t hit the nucleus?

Bohr Model

Bohr claimed that electron can have only certain energy levels.

The way we describe the energy levels is by using quantum numbers ‘n’

Only orbits where n =positive integer are permitted.

Energy of quantized state

n = 1

n = 2

Quantum States

Further from the nucleus means more energy

There is no “in between” energy

Energy of one electron: E of an electron:

En 13.6eV

n2

Guided Practice (2 minutes)

Calculate the energy of an electron on the second energy level, E2, of the hydrogen atom.

What equation should we use for this?

En =-13.6/n2

What are the knowns and unknowns???

N = 2

E2 = ???

-3.4eV

Quantum States

Can we have an energy level of 2.5?

NO!!!!

Radius of electron orbits:

211 )103.5( nmxrn

Practice (2 minutes)

Calculate the radius of an electron on the third energy level,

E3, of the hydrogen atom.

47.7x10^-11m

Ionization The ionization energy is equal to the

negative energy of the electron

Ionization energy is the energy to remove an electron.

Eionization = -En

Practice

What is the ionization energy of a hydrogen atom that is in the n = 3 excited state?

1.51 eV

Classwork

Spend the rest of class working on “Bohr Atom Classwork”.

It is due Thursday.

For Problems 5 and 6 the energy should be negative.

Do Now (3/26/14) (5 minutes):

1)What is the energy associated with an electron in the ground state of a hydrogen atom?

2) What is the energy change when an electron drops from E5 to E1 in an excited hydrogen atom?

Do Now Quiz (5 Minutes)

What is the energy change of an electron in the fourth energy level of a hydrogen atom that drops to the second energy level?

211 )103.5( nmxrn

En 13.6eV

n2

E- E nionization

Talk with your group (1 minute) When an electron drops from a higher

state to a lower state, what happens to it’s energy?

The electron’s energy decreases!

The Bohr Model When an electron loses energy and drops to a lower state, a photon is released with energy:

statelower statehigher photon E–E hc

E

hf

E of photon: Another way to look at it:

22

6.136.13

lowerstateehigherstat n

eV

n

eV

How can I visualize this?

Example (3 minutes):

An electron drops from the 6th energy state to the 3rd. What is the energy of the photon emitted?

1.13eV

Classwork

Spend the rest of class working on “The Bohr Atom”.

It is due Tuesday.By the end of class you need to have a minimum of 6 problems completed. This will be worth points towards the assignment.

Do Now (3/27/14) (5 minutes):

1)What is the energy of the photon emitted by an electron that jumps from

the sixth energy level to the second energy level?

Different types of Atoms So far, we have been working with

atoms of a certain element. What type of atoms have we been studying

so far this week?

Hydrogen Atoms

Hydrogen-like Atoms (atoms that have been ionized so that they

have one electron left)

2

2 )6.13(

n

eVZEn

Where Z is the Atomic Number

Hydrogen-like Atoms (atoms that have been ionized so that they

have one electron left)

Where Z is the Atomic Number

)100529(. 92

mxZ

nrn

Other Atoms The previous equations were for “Hydrogen-

Like” Atoms (atoms that have been ionized so that they have

one electron left)

Will these equations work for all atoms?

NO

Practice (3 minutes)

Calculate the radius of an electron on the third energy level, E3, of an ionized helium atom. (Z =

2)

2.38x10-10m

Guided Problem(7 minutes):

1)What is the frequency of the photon emitted by an electron that jumps from

the third energy level to the second energy level?

What are the givens and what are we solving for?

Photon starts at E3

Photon falls to E2

We want to solve for the FREQUENCY of the PHOTON

Guided Problem (7 minutes) We want to solve for the

FREQUENCY of the PHOTON

What is an equation we’ve learned previously for the Frequency of a

Photon?

E = hf Is this energy in Joules or eV?

It must be in Joules!!!

Guided Problem (7 minutes)

E = hf

If we want to solve for frequency, what other variable in this equation do we

need to find?

The energy of the photon!!!

Guided Problem (7 minutes)

With our givens of, E3 and E2, how can we solve for the energy of the

photon?

statelower statehigher photon E–E E hf

Guided Problem (7 minutes) Let’s Summarize

We want to solve for ____??? The Frequency of the photon

The equation we use for frequency is???E = hf

This equation gives us the energy of the photon

Guided Problem (7 minutes) Let’s Summarize

How do we get the energy of the photon?

statelower statehigher photon E–E E hf

Guided Problem (7 minutes) Let’s Solve

hf /)E–(E statelower statehigher

Hzf 1410*.564

hf /)J10*-5.44–J10*(-2.4 -19-19

Quiz Review Monday we are going to do a Gallery

Walk. Each table will be assigned a problem off the quiz review sheet.

You will write out your solution on a blank piece of printer paper. It doesn’t have to be colorful just clear and easy to read.

Quiz Review

BRING YOUR COMPLETED SOLUTION WITH YOU

MONDAY

You will not get more class time to write out your solution

Rubric

You will get three minutes per question to look over it and grade their solution

Today’s Classwork Work on your Quiz Review sheet

Once everyone at a table has finished two problems I will assign you a problem off the

Quiz Review for Monday.

You may check your answer with the key and when you have the right answer I can give

you printer paper.

Do Now (3/31/14) (5 minutes):

List at least three different equations and come up with two problem solving tips that should be on your notecard for Tomorrow’s

Quiz.Ephoton= hf = Ehigher state- Elower state

En = -13.6/n2 rn = n2*(5.3x10-11)

When an photon is released, Energy Change is Higher – Lower

Further the electron is away more required energyIf Ephoton> Eionizization= than the electron is ejected

2

2 )6.13(

n

eVZEn

)100529(. 9

2

mxZ

nrn

Gallery Walk (5 Minute Prep) Take out your Quiz Review Solution

You will move from one table to another in chronological order.

Three minutes per table

If you finish early at a table, Bonus points if you give suggestions on how to improve a solution.

Gallery Walk Check each groups’ solution against the answer key provided for you.

Bonus points if you give suggestions on how to improve a solution.

Fill out the rubric for each group, make sure to leave your slot on the rubric blank.

Transition (1 Minute)

Pass on your Rubrics and take out any notes you wish to use for the Multiple Choice Review

Multiple Choice

1) When does an electron emit a photon?a) when it reverses its movement

around the nucleusb) when it stays in the same energy

level c) when it jumps from the fourth to

the third energy leveld) when it jumps from first to the

second energy level Answer: C

Multiple Choice

2) In which energy level transition will the emitted photon have the highest frequency?

A. from n = 5 to n = 1 B. from n = 4 to n = 1 C. from n = 3 to n = 1 D. from n = 2 to n = 1

Answer: A

Multiple Choice

3) What is the frequency of the photon emitted when an electron drops from E5 to E4 in an excited hydrogen atom?

A. 3.55 x 1014 HzB. 4.89 x 1013 HzC. 7.39 x 1013 HzD. 5.86 x 1014 Hz

Answer: C

Multiple Choice

4) What is the radius of the orbital associated with the energy level E5 of the hydrogen atom?

A. 1.91 x 10-10 mB. 1.33 x 10-9 m C. 1.33 x 10-10 mD. 1.91 x 10-9 m

Answer: B

Multiple Choice

5) A hydrogen atom electron has an energy of -3.4 eV when it is in the second energy level. What is the minimum energy necessary to ionize the hydrogen atom if the electron is in the second energy level?

A. 13.6 eV C. 1.51 eVB. 3.4 eV D. 1.02 eV

Answer: B

Quiz Review

Spend the rest of class finishing up your Quiz Review Paper.

Make sure to make a notecard!!!

I will be here after school today until 4pm.

Rubric

You will get three minutes per question to look over it and grade their solution

The Bohr Model of the Atom

3/10/14

Do Now (3/29/12):An electron is in energy state #5.

1.What is the radius of the orbit?

2.What is the energy of the electron?

Energy Level Diagrams Minimum energy to remove an electron is

binding energy or ionization energy. 13.6eV – energy required to remove an

electron from the lowest state E1= -13.6eV up to E=0.

Lyman series, Balmer series, Paschen series for hydrogen atoms. – pg 848.

Practice: Complete the Bohr Atom classwork Check your answers with the key at the front

of the room When you get 100%, submit your work and

begin to work on your homework

Energy Transitions in Atoms 

Energy of photon = Energy lost by electron                            hf  = Ei - Ef

Calculating Wavelengths of Emitted Light

hf  = Ei - Ef E3  --->  E2:Ei  =  - 1.51 eVEf  =  - 3.40 eV------------------------------hf   = - 1.51 - (-3.40)      = 1.89 eV------------------------------l = (1240 eV-nm) / E

   = 1240 / 1.89   = 656 nm