Kendrickchemistry.weebly.com



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 Rutherford-

Chadwick model of the atom.

Rutherford-Chadwick Model Bohr Model

? What is the main difference between the Rutherford-Chadwick

model and the Bohr model?

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.

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 Hydrogen Atom #2 Hydrogen Atom #3 Hydrogen Atom #4

The electron: The electron: The electron: 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 releases energy as releases energy as releases energy as

light - color_______ light – color_______ light – color_______ 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?

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?

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 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 frequency wavelength

m/s s-1 or 1/s 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 speed of light frequency wavelength

J•s m/s s-1 or 1/s m

Constants:

c = speed of light = 3.00 x 108 m/s

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

[pic]

-----------------------

Energy Levels

Vocabulary!

Vocabulary!

Vocabulary!

Vocabulary!

Vocabulary!

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download