CP Chemistry
Worksheet 2.1
1.
Name ________________________
Date _________ Class _________
Draw three waves with wavelengths of x, 2x, and 4x.
4x
10. What causes an atom to emit light?
Atoms emit light when they absorb energy. It can be
electrical energy, heat energy or through a chemical
reaction.
2x
11. What do we mean by the speed of EM radiation, how
fast is it? All EM radiation travels at 3.0 x 108 m/s.
x
2.
Order the wavelengths from question #2 from lowest to
highest frequency.
4x, 2x, x
3.
Order the wavelengths from lowest to highest energy
and explain your answer.
4x, 2x, x
4.
Microwaves are used to transmit information. What is
the wavelength of a microwave having a frequency of
3.44x109 Hz?
𝑐
3.0 𝐸 8 𝑚/𝑠
𝜆= =
= .087 m
𝜈
5.
3.44𝐸9 𝐻𝑧
An X-Ray has a wavelength of 1.15x10-10m. What is it’s
frequency?
𝑐
3.0 𝐸 8 𝑚/𝑠
𝜈= =
= 2.61 x 1018 Hz
𝜆
1.15 𝐸−10 𝑚
12. Why do we say atomic spectra are like fingerprints of
the elements?
Atomic line spectra or just emission spectra represent
the unique electron transitions within each atom;
therefore, they are unique to that atom, like our
fingerprints are to us.
13. Describe Bohr’s model of the atom.
Bohr proposed that the electrons travel around the
nucleus in circular orbits and they are at discrete
distances from the nucleus. When e- fall from a higher
“n” to a lower “n” energy is released in the form of a
photon of light corresponding to the distance the e- fell.
14. How much energy would an electron release if it fell
from n=3 to n=2?
−2.18 𝐸−18 𝐽
∆𝐸 = 𝐸3 − 𝐸2
𝐸𝑛 =
2
𝐸3 =
𝐸2 =
6.
How much energy does a photon with a wavelength of
250nm have?
first convert nm to m= 2.50 x 10-7 m
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 =
7.
𝜆
𝑚
=
(3.0 𝐸 8 𝑠 )(6.626 𝐸−34 𝐽∙𝑠)
2.50 𝐸−7 𝑚
= 7.95 𝑥 10−19 𝐽
What is the frequency of a photon that has an energy of
4.0 x 10-19 J
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 = ℏ ∙ 𝜈 𝑟𝑒𝑎𝑟𝑟𝑎𝑛𝑔𝑒
𝜈=
8.
𝑐 ∙ℏ
𝐸
ℏ
=
4.0 𝐸−19 𝐽
6.626 𝐸−34 𝐽𝑠
= 6.04 𝑥 1014 𝐻𝑧
Why does ultraviolet light cause more damage to our
skin than visible light? On the EM spectrum UV light is to
the left of blue and violet; therefore, it has more energy
associated with it.
−2.18 𝐸−18 𝐽
32
−2.18 𝐸−18 𝐽
22
∆𝐸 = −5.45 𝑥
𝑛
= −2.42 𝑥 10−19 𝐽
= −5.45 𝑥 10−19 𝐽
10−19 𝐽
− (−2.42 𝑥 10−19 𝐽) = −3.03𝑥10−19 𝐽
15. How much energy does it take to excite an electron
from n= 3 to n=4?
−2.18 𝐸−18 𝐽
∆𝐸 = 𝐸4 − 𝐸3
𝐸𝑛 =
2
𝐸3 =
𝐸4 =
−2.18 𝐸−18 𝐽
32
−2.18 𝐸−18 𝐽
42
𝑛
= −2.42 𝑥 10−19 𝐽
= −1.36 𝑥 10−19 𝐽
∆𝐸 = −1.36 𝑥10−19 𝐽 − (−2.42 𝑥 10−19 𝐽) = 1.06𝑥10−19 𝐽
16. What happens to an electron as it absorbs a photon of
light?
It is “excited” to a higher energy level.
17. What is a “packet” of EM energy called?
A quanta, specifically a photon.
18. What is the range of wavelengths of visible light?
Approximately 700 nm to 400 nm.
9.
As the frequency of light increases what happens to its
energy? frequency and energy are directly related, think
about the equation 𝐸 = ℏ ∙ 𝜈
19. Define Electromagnetic radiation.
Range of all energies from the very short wavelength
like gamma rays to the very long wavelength like radio
waves.
20. Describe the mathematical relationship between
wavelength and frequency.
𝑐 = 𝜆 ∙ 𝜈, inversely related
(c)
Does the electron gain or lose energy in the
transition?
The positive sign indicates that energy is being
absorbed in order to transition from a low “n” to a
higher “n”.
(d)
What is the change in energy of the electron?
2.04 x 10-18 J
21. Give two examples of electromagnetic radiation with
long wavelengths. radio waves, microwaves
1.
Red has a longer wavelength because the distance
from crest to crest is greater than blue light.
22. Which is the longer wavelength: blue light or red light?
Explain.
27. A hydrogen electron transitions from n = 9 to n = 7.
(a)
What is the energy of the electron when n = 9.
See question #14 for explanation.
-2.69 x 10-20 J
(b)
Xray
UV
yellow
IR
TV
23. List the following types of electromagnetic radiation in
order of decreasing frequency:
(a)
X rays used for medical purposes
(b)
infrared from a heating lamp
(c)
TV signal from Channel 12
(d)
yellow traffic light
(e)
ultraviolet light that causes sunburn
24. Of the following regions of the electromagnetic
spectrum, which one has the shortest wavelength?
a. microwaves
b. infrared radiation
c. X-Ray
d. ultraviolet rays
e. radio waves
f. gamma rays
25. Calculate the missing value.
Photon energy
Wavelength
3.25 x 10-18J
1.58 E -18 J
6.11 E -8 m
1.26 x 10-7m
What is the energy of the electron when n = 7
-4.45 x 10-20 J
(c) What is the change in energy for the transition?
-1.76 x 10-20 J
(d)
Is energy absorbed or released during the
transition? The negative sign indicates that
energy is being released, which is always the case
when an electron transitions from a higher “n” to
a lower “n”.
(e) What is the wavelength of the light emission?
∆𝐸 𝑖𝑠 𝑒𝑞𝑢𝑎𝑙 𝑡𝑜 𝑡ℎ𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑡ℎ𝑒 𝑝ℎ𝑜𝑡𝑜𝑛 𝑒𝑚𝑖𝑡𝑡𝑒𝑑.
ℏ∙𝑐
ℏ∙𝑐
ℏ∙𝑐
𝑟𝑒𝑎𝑟𝑟𝑎𝑛𝑔𝑒; 𝜆 =
=
𝜆
𝐸𝑝ℎ𝑜𝑡𝑜𝑛
−1.76𝑥10−20 𝐽
= 1.13 𝑥 10−5 𝑚
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 =
28. Determine the energy of 1 mol of photons for each kind
of light.
(a)
infrared radiation (1500 nm)
First covert wavelength to meters:
1𝑚
1500𝑛𝑚 ×
= 1.5 𝑥10−6 𝑚
9
1 𝑥10 𝑛𝑚
Now calculate energy per photon:
6.60 x 10-19J
3.01 E -7 m
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 =
𝑐 ∙ℏ
𝜆
=
𝑐 ∙ℏ
1.5 𝑥10−6 𝑚
= 1.32 𝑥 10−19 𝐽
Convert energy per photon to energy per mole
5.76 E -19 J
345 nm
×
1.32 𝑥 10−19 𝐽 6.02 𝑥 1023 𝑝ℎ𝑜𝑡𝑜𝑛𝑠
×
= 79,464 𝐽/𝑚𝑜𝑙
1 𝑝ℎ𝑜𝑡𝑜𝑛
1 𝑚𝑜𝑙
(b)
26. A hydrogen electron transitions from n = 1 to n = 4.
(a)
What is the electron's energy at n = 1?
See question #14 for explanation.
-2.18 x 10-18 J
(b)
What is the electron's energy at n = 4?
-1.36 x 10-19 J
visible light (500 nm)
239,331 J/mol
(c)
ultraviolet radiation (150 nm)
797,770 J/mol