The Bohr Model

Report
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?


Which particle has a negative charge?


Proton
Electron
Which particle has a neutral charge?

Neutron
Ernest Rutherford


1911 Ernest Rutherford
Nucleus of an atom was:
very dense,
 veryis
small
What
in-between the
 positively
charged.
Nucleus
and
the
 Electrons were located
Electrons?
outside the nucleus.

Empty Space!!!
View of atomic Structure in early 1900’s
electrons traveled around the nucleus
in orbits, like the planets
+
Electron
orbit
Classical (before 1900)
physics could not explain
why electrons don’t fall into
the nucleus
Video

- How did J.J. Thomson describe the atom?


- What model did Rutherford use to describe the
atom?


Plum Pudding Model
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.
2.
1.
Describe the structure of an
atom.
Draw a picture of an atom.
(I will need three volunteers to draw their atom)
Rutherford’s Model
How did Rutherford describe the motion of
electrons around the nucleus?
+
Electron
orbit
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.
Energy of quantized state
 The
way we describe
the energy levels is by
using quantum
numbers ‘n’
 Only orbits where
n =positive integer
are permitted.
n=2
n=1
Quantum States
 Further
from
the nucleus
means more
energy
 There is no “in
between”
energy
Energy of one electron:

E of an electron:
13.6eV
En 
2
n
Guided Practice (2 minutes)
Calculate the energy of an electron on
the second energy level, E2, of the
hydrogen atom.
What are the What equation
should we use for
knowns and
this?
unknowns???
-3.4eV
N=2
E2 = ???
En =-13.6/n2
Quantum States
 Can
we have
an energy level
of 2.5?
 NO!!!!
Radius of electron orbits:
11
rn  (5.3x10 m)n
2
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?
11
rn  (5.3x10 m)n
2
Eionization  - En

13.6eV
En 
2
n
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:
hc
E photon  hf 
 E higher state – E lower state

E of photon:

Another way to look at it:
 13.6eV  13.6eV

2
2
nhigherstat e
nlowerstate
How can I visualize this?
Example (3 minutes):
 An
th
6
electron drops from the
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)
Z (13.6eV )
En 
2
n
2
Where Z is the Atomic Number
Hydrogen-like Atoms

(atoms that have been ionized so that they have one
electron left)
2
n
9
rn  (.0529x10 m)
Z
Where Z is the Atomic Number
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?
Ephoton  hf  Ehigher state – Elower state
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?
Ephoton  hf  Ehigher state – Elower state
Guided Problem (7 minutes)

Let’s Solve
f  (Ehigher state – Elower state ) / h
f  (-2.4*10 J – -5.44*10 J) / h
-19
-19
f  4.56*10 Hz
14
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
2
En = -13.6/n2
2
Z
(13.6eV )
n
9
2
-11
En 
rn = n *(5.3x10 )
rn  (.0529x10 m)
n2
Z
When an photon is released, Energy Change is Higher – Lower
Further the electron is away more required energy
If Ephoton> Eionizization= than the electron is ejected
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
nucleus
b) when it stays in the same energy level
c) when it jumps from the fourth to the third
energy level
d) 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 Hz
B. 4.89 x 1013 Hz
C. 7.39 x 1013 Hz
D. 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 m
B. 1.33 x 10-9 m
C. 1.33 x 10-10 m
D. 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 eV
B. 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 eV
Ef = - 3.40 eV
-----------------------------hf = - 1.51 - (-3.40)
= 1.89 eV
----------------------------- = (1240 eV-nm) / E
= 1240 / 1.89
= 656 nm

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