Download The Bohr Model of the Atom By the end of this lesson, I will be able

The Bohr Model of the Atom
By the end of this lesson, I will be able to:
 Explain the following terms: energy level, atomic emission spectrum,
wavelength, frequency, speed of light, energy, wave, photon,
Planck’s constant.
 Relate the pattern in an element’s atomic emission spectrum to the
atomic structure of the atom.
 Compare the relative sizes of the wavelength, frequency, and energy
of different colors of light.
 Calculate the wavelength, frequency, and energy of different colors of
light.
Compare the Bohr model of the atom to the earlier RutherfordChadwick model of the atom.
Energy Levels
Rutherford-Chadwick Model
Bohr Model
? What is the main difference between the Rutherford-Chadwick
model and the Bohr model?
Vocabulary!
Energy level: a specific electron orbit around the nucleus
of the atom – an electron must gain energy to move to a
higher energy level.
Part 1: Atomic Emission Spectra
The presence of energy levels in the atom, explains the origin
of hydrogen’s atomic emission spectrum.
Vocabulary!
The atomic emission spectrum of an atom is a specific
pattern of colored lines that is seen when the light
emitted from a sample of identical superheated atoms
is viewed through a prism.
Look at the handout titled “Atomic Emission Spectra”.
The top section of this handout shows the atomic emission spectra
of several elements including hydrogen.
The pattern of colored lines is different for each element and can
be used to identify the elements in a mixture.
The bottom section of the handout shows the atomic emission
spectra of four mixtures of elements.
For each mixture, compare its atomic spectrum to the atomic
spectra of the individual elements in the top section of the
handout.
? Use the atomic spectra patterns to identify the elements in each
of the mixtures in the bottom section of the “Atomic Emission
Spectra” handout.
Mixture A Elements
Mixture B Elements
Mixture C Elements
Mixture D Elements
In order to understand how Bohr’s model explains the atomic
emission spectrum of hydrogen, we are going to create large-scale
models of some hydrogen atoms.
Your teacher has drawn the energy levels of an atom on the floor. Four
of your classmates will take turns pretending to be hydrogen’s single
electron. (They have each been provided with secret instructions!)
Each of your four classmates will show a different way that hydrogen’s
one electron can move between energy levels and what happens when
it does.
? Record what happens to each electron on the atom diagrams below.
The energy levels are each numbered.
Hydrogen Atom #1
The electron:
Hydrogen Atom #2
The electron:
Hydrogen Atom #3
The electron:
Hydrogen Atom #4
The electron:
starts in level_____
starts in level_____
starts in level_____
starts in level_____
absorbs energy
absorbs energy
absorbs energy
absorbs energy
jumps to level_____
jumps to level_____
jumps to level_____
jumps to level_____
falls to level_____
falls to level_____
falls to level_____
falls to level_____
releases energy as
light - color_______
releases energy as
light – color_______
releases energy as
light – color_______
releases energy as
light – color_______
Compare the colors emitted by each of the electrons above to the
atom emission spectrum for hydrogen on the “Atomic Emission
Spectra” handout.
? What do you think is the origin of the four colored lines in the
atomic emission spectrum of hydrogen?
Part 2: The Nature of Light
In order to understand Bohr’s model, we need to learn a little bit
about the nature of light and color.
 Open the envelope labeled “Colors of Light Card Set”.
This card set contains cards that illustrate the energy, wavelength,
frequency, and speed of light of different colors of light.
The symbols that are used for wavelength, frequency, energy, and
the speed of light are indicated in parenthesis.
 Locate the card that describes red light.
Look at the wavelength section of the card.
? What is the symbol for wavelength?
? Based on the illustration, what do you think is the
definition of the wavelength of a wave?
Vocabulary!
Wavelength: the distance between the adjacent peaks
of a wave.
Look at the frequency section of the card.
? What is the symbol for frequency?
? Based on the illustration, what do you think is the
definition of the frequency of a wave?
Vocabulary!
Frequency: the number of wavelengths that pass a
designated point in one second.
 Arrange the cards as they appear in a rainbow: red,
orange, yellow, green, blue, violet
? What happens to the size of the wavelength as you
move from red towards violet?
? What happens to the size of the frequency as you move
from red towards violet?
? What is the relationship between wavelength and
frequency? (i.e. Do they both increase or decrease
together or does one decrease when the other one
increases?)
? What is the symbol for energy?
? What happens to the amount of energy in the wave as
you move from red towards violet?
? What is the symbol for the speed of light?
? Compare the speed of light for each color. Is the speed
of light the same or different for different colors of
light?
Light appears to behave as both a wave and a particle.
Wave
Vocabulary!
Particle (photon)
Wave-Particle Duality: Light appears to be able
to behave as both a particle (photon) and a wave.
Photon: A particle of light
Part 3: Light Calculations
 The relationship between wavelength, frequency, and the speed of
light is illustrated by the following formula.
Formula in Words:
speed of light = (frequency)(wavelength)
Formula in Symbols:
c = fλ
Units:
speed of light
m/s
frequency
s-1 or 1/s
wavelength
m
Constants:
c = speed of light = 3.00 x 108 m/s
The following example shows how to calculate the wavelength of
a light wave when you are given the frequency.
What is the wavelength of a wave of green light with a
frequency of 6.01 x 1014 s-1?
Formula: c = fλ
Rearrange the Equation to Isolate λ:
c = fλ
c=λ
f
Substitute Values:
(3.00 x 108 m/s) = λ
(6.01 x 1014 s-1)
Divide:
λ = (3.00 x 108 m/s) = 4.99 x 10-7 m
(6.01 x 1014 s-1)
? Try it!
What is the wavelength of light with a frequency of
7.66 x 1014 s-1?
Formula:
Rearrange the Equation to Isolate λ
Substitute Values:
Divide:
The following example shows how to calculate the frequency of
a light wave when you are given the wavelength.
What is the frequency of a wave of violet light with a
wavelength of 3.88 x 10-7 m?
Formula: c = fλ
Rearrange the Equation to Isolate f:
c = fλ
c=f
λ
Substitute Values::
(3.00 x 108 m/s) = f
(3.88 x 10-7 m)
Divide:
f = (3.00 x 108 m/s) = 7.73 x 1014 s-1
(3.88 x 10-7 m)
? Try it!
What is the frequency of light with a wavelength
of 5.20 x 10-7 m?
Formula:
Rearrange the Equation to Isolate f
Substitute Values:
Divide:
 The relationship between the wavelength, frequency, and energy
of a wave is illustrated by the following two formulas.
Formula in Words:
Formula in Words
energy = (Planck’s constant)(frequency)
energy = (Planck’s constant)(speed of light)
wavelength
Formula in Symbols:
Formula in Symbols:
E = hf
E = hc
λ
Units:
Planck’s constant
J•s
speed of light
m/s
frequency
s-1 or 1/s
Constants:
c = speed of light = 3.00 x 108 m/s
wavelength
m
h = Planck’s constant = 6.63 x 10-34 J•s
The following example shows how to calculate the energy of
light when you are given the frequency.
What is the energy of a photon of light with a frequency
of 5.00 x 1014 s-1?
Formula: E = hf
Substitute Values:
E = (6.63 x 10-34 J•s)(5.00 x 1014 s-1)
Multiply:
E = (6.63 x 10-34 J•s)(5.00 x 1014 s-1) =
3.32 x 10-19 J
? Try it!
What is the energy of violet light with a frequency of
7.50 x 1014 s-1?
Formula:
Substitute Values:
Multiply:
The following example shows how to calculate the energy of
light when you are given the wavelength.
What is the energy of a photon of light with a wavelength
of 5.62 x 10-7 m?
Formula: E = hc
λ
Substitute Values:
E = (6.63 x 10-34 J•s)(3.00 x 108 m/s)
5.62 x 10-7 m
Multiply and Divide:
E = (6.63 x 10-34 J•s)(3.00 x 108 m/s) =
5.62 x 10-7 m
3.54 x 10-19 J
? Try it!
What is the energy of violet light with a wavelength of
7.20 x 10-7 m?
Formula:
Substitute Values:
Multiply and Divide:
 Ask your teacher for an “Excite” game board , a pair of dice, and a
set of game cards. You will also need the “Game Card Answer
Sheet” and a small object to use as a game piece.
 Practice calculating wavelength, frequency, and energy by playing a game
of “Excite” as described below.
“Excite!” Game Rules
1. Separate the game cards into stacks of “Light” cards and “Energy”
cards.
2. The first player rolls the dice and advances their game piece the
indicated number of spaces.
3. If the player lands on a “Light” space, he or she draws a “Light” card. If
the player lands on an “Energy” space, he or she draws an “Energy”
card.
4. The player calculates the answer to their card and records the answer
on their “Game Card Answer Sheet”. The other players should also
calculate the answer at the same time.
5. The other players must agree that current player’s answer is correct. If
the answer is incorrect, the player loses a turn. Disputes will be settled
by the teacher.
6. If a player lands on a space at the bottom of a ladder, he or she must
climb back to the space at the top of the ladder. If a player lands on a
space at the top of a chute, he or she gets to slide down to the space
at the bottom of the chute.
7. The player that gets the last space on the game board first is the
winner.
Game Card Answer Sheet
Show your work for each card in the boxes below. Write the card
number of each card in the smaller box. You do not have to
use all of the boxes.
Vocabulary
Energy Level: a specific electron orbit around the nucleus of the atom an electron must gain energy to move to a higher energy level.
Atomic Emission Spectrum: a specific pattern of colored lines that is
seen when the light emitted from a sample of identical superheated
atoms is viewed through a prism.
Wavelength: the distance between adjacent peaks in a wave.
Frequency: the number of wavelengths that pass a designated point in
one second
Speed of Light: the speed of all colors of light – the speed of light is
equal to 3.00 x 108 m/s.
Energy: absorbed by electrons causing them to become “excited” and
jump to higher energy levels.
Light Wave: a type of electromagnetic energy – waves transfer energy.
Photon: a particle of light
Planck’s Constant: a constant needed to calculate the energy of a
photon of light – Planck’s constant is equal to 6.63 x 10-34 J•s.
The Bohr Model of the Atom
Study Sheet
Atomic Emission Spectra
Speed of Light Calculations
Energy Calculations
Copyright © Shari Kendrick