Quantum Mechanics-Chemistry
Of these electromagnetic waves, which has the longest wave length, greatest energy, greatest
frequency, lowest amplitude? ️1. Wavelength is the distance between identical points on successive
waves. Wave B has the longest wavelength.
2. Frequency is the number...
Of these electromagnetic waves, which has the longest wave length, greatest energy, greatest
frequency, lowest amplitude? ✔️1. Wavelength is the distance between identical points on successive
waves. Wave B has the longest wavelength.
2. Frequency is the number of wavelengths that pass per unit time. Since all electromagnetic waves
move at the same speed (the speed of light), equal distances represent equal amounts of time. In the
same distance, wave A shows 2.5 wavelengths, wave B shows 1.25 wavelengths, and wave C show 4
wavelengths.
3. Energy is directly proportional to frequency. Since wave C has the greatest frequency, it also has the
greatest energy.
4. Amplitude is the height of a peak (or depth of a trough). Wave A has the lowest amplitude.
which has the longest wavelength? Ultraviolet light or radio radiation? ✔️Radio Radiation
which has the greatest energy and frequency? Ultraviolet light or radio radiation ✔️UV Light (recall that
frequency and energy are proportional to each other)
The frequency of the middle B note on a piano is 493.88 Hz. What is the wavelength of this note in
centimeters? The speed of sound in air is 343.06 m/s. ✔️1. The wavelength, λ, and frequency, ν, of
waves are related by the formula: SPEED= λ(ν).
2. Rearrange the formula to: λ=SPEED/v
3. Substitute the known values. Remember that the unit Hz is equivalent to s-1.
4. Now change from meters to cm.
Microwave ovens emit microwave energy with a wavelength of 12.6 cm. What is the energy of exactly
one photon of this microwave radiation? ✔️1. We will use the equation: E=hc/λ
2. h=Planck's Constant: 6.626×10^(-34) J∙s
3. c= speed of light = 3.00×10^8 m
4. λ=12.6 cm= 0.126 m
, A certain shade of blue has a frequency of 7.20 × 1014 Hz. What is the energy of exactly one photon of
this light? ✔️1. We will use the equation E=hf
2. h=Planck's Constant: 6.626×10^(-34) J∙s
3. f=Frequency (7.20 × 1014 Hz)
How many photons are produced in a laser pulse of 0.794 J at 487 nm? ✔️1. We will use the equation:
E=ħv
v=frequency and in order to find the frequency we need to use the wavelength, thus: λ⋅ν=c. To find the
frequency we simply rearrange the equation to v=c/λ
λ = wavelength = 487 nm = 487x10^-7 m
2. Now use the equation E=hc to find the single photon where:
E = energy per photon...
ħ = plancks constant = 6.626x10^-34 J s
c = speed of light = 3.00x10^8 m/s
3. Now we know the energy the laser pulse produced. Divide 0.794J by the response from the E=hc
equation.
A metal foil has a threshold frequency of 5.45× 1014 Hz. Which of the colors of visible light have enough
energy to eject electrons from this metal? ✔️1. find the wavelength associated with 5.45× 1014 Hz.
(c=λ⋅ν)
2. Rearrange the equation: λ=c/v (Note that a Hz is equal to an inverse second (s-1).
3. Convert to nanometers.
Absorption occurs when an electron goes from ✔️a lower-energy shell to a higher-energy shell. For
example, the transitions from n=1 to n=3 and n=3 to n=5 result in the absorption of light.
Emission occurs when an electron goes from ✔️a higher-energy shell to lower-energy shell. For
example, the transitions from n=2 to n=1 and n=3 to n=2 result in the emission of light.
The principal quantum number, n, indicates the relative energy of a shell. However, the difference in
energy between n=1 and n=2 is not the same as the difference in energy between n=2 and n=3. Thus,
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