CHEM 112A Notes
Module 4 - Atoms
Partial pressure: Ptotal = P1 + P2 …
Mole fraction: xi: number of moles i / total number of moles of gas
Collecting over water: Ptotal = PH2O +
PO2
Van der waals: P = (RT/V - b) - a / V2
4.1 - Light
Wavelength, Symbol: λ (lambda)
SI unit: meters (m)
Frequency, Symbol: v (nu)
SI unit: hertz or 1/seconds (Hz = 1/s = s-1)
Speed of light (in a vacuum), Symbol: c = 2.9979 x 108 ms-1
SI unit: meters/second (m/s = ms-1)
Light:
● Has an electric field and a magnetic field are perpendicular to each other but
moving along the same direction of travel
● As you increase frequency of waves, you decrease wavelengths, and vice versa
Relationship between frequency of wavelength: c = λv
Waves - Simplistic
● Periodic function
● Displaced over space and time
● Interference patterns, diffraction
4.2 - Blackbody Radiation
Blackbody: an object that emits light at all wavelengths.
What is making the light?
, ● Heat = transfer of kinetic energy
● Atom in the metal use KE to vibrate
● Vibrations generate light
● Max Planck: determined that atoms are quantized
● Energy released gas only certain allowed values (quantized)
Planck’s Equation: E = nhv
E = energy (J)
n = integer (1,2,3...)
h = 6.626 x 10-34 Js (Plank’s Constant)
v= frequency (1/s, Hz)
Quantization
● Predicts distributions accurately at all wavelengths
● Not observed before since energy is quantized on a tiny scale
4.3 - Photoelectric Effect
Photoelectric effect: when light hits a piece of metal, electrons are ejected
● Increasing intensity = current increases
● Increasing wave4 length = current decreases, no more electrons
Albert Einstein: ΔE = hv
● Greater the energy, greater the frequency
● Smaller the wavelength, greater the energy
Example: determine the energy, in joules per photon, of radiation of frequency 7.38 x
10^15 Hz.
ΔE = hv
= (6.626 x 10^-34 Js) (7.38 x 10^15 s-1)
= 4.9 x 10^-18 J
, Velocity: Ephoton = ɸ + KE or hv = hv0 + ½mu2
ɸ = threshold energy
hv = incident photon
m = mass of electron
u = speed of electron
KE = kinetic energy
hv0 = threshold frequency (required)
Example: the minimum energy required to cause the photoelectric effect in
potassium metal is 3.69 x 10^-19 J. If 420 nm radiation is shone on potassium will
electrons be ejected? If yes, what is their velocity?
h= 6.626 x 10^-34 Js 1 nm = 1 x 10-9 m
me = 9.109 x 10^-31 kg 420 nm = 4.2 x 10-7 m
c= 2.9979 x 108 ms-1 ΔE = hv = hc/λ = (6.626 x 10^-34 Js) (2.9979 x 108 ms-1)
/
ɸ = 3.69 x 10^-19 J (4.2 x 10-7 m)
= 4.7 x 10^-19 J --> since this is larger than ɸ, photons will be ejected
Velocity: Ephoton = ɸ + KE
4.7 x 10^-19 J = 3.69 x 10^-19 J + ½ (9.109 x 10^-31 kg) u2
1.01 x 10^-19 J = (4.5545 x 10^-31 kg) u2
2.217 x 10^11 J/kg = u2
4.8 x 10^5 m/s = u
4.4 - Atomic Spectra
Balmer Series
● 4 wavelengths only visible
λ W (cm-1)
Hα Red 6563 15234 n1 = 3
Hβ Green blue 4862 20565 n1 =
4
Hγ Blue 4342 23033 n1 = 5
Hδ Violet 4103 24374 n1 = 6
Module 4 - Atoms
Partial pressure: Ptotal = P1 + P2 …
Mole fraction: xi: number of moles i / total number of moles of gas
Collecting over water: Ptotal = PH2O +
PO2
Van der waals: P = (RT/V - b) - a / V2
4.1 - Light
Wavelength, Symbol: λ (lambda)
SI unit: meters (m)
Frequency, Symbol: v (nu)
SI unit: hertz or 1/seconds (Hz = 1/s = s-1)
Speed of light (in a vacuum), Symbol: c = 2.9979 x 108 ms-1
SI unit: meters/second (m/s = ms-1)
Light:
● Has an electric field and a magnetic field are perpendicular to each other but
moving along the same direction of travel
● As you increase frequency of waves, you decrease wavelengths, and vice versa
Relationship between frequency of wavelength: c = λv
Waves - Simplistic
● Periodic function
● Displaced over space and time
● Interference patterns, diffraction
4.2 - Blackbody Radiation
Blackbody: an object that emits light at all wavelengths.
What is making the light?
, ● Heat = transfer of kinetic energy
● Atom in the metal use KE to vibrate
● Vibrations generate light
● Max Planck: determined that atoms are quantized
● Energy released gas only certain allowed values (quantized)
Planck’s Equation: E = nhv
E = energy (J)
n = integer (1,2,3...)
h = 6.626 x 10-34 Js (Plank’s Constant)
v= frequency (1/s, Hz)
Quantization
● Predicts distributions accurately at all wavelengths
● Not observed before since energy is quantized on a tiny scale
4.3 - Photoelectric Effect
Photoelectric effect: when light hits a piece of metal, electrons are ejected
● Increasing intensity = current increases
● Increasing wave4 length = current decreases, no more electrons
Albert Einstein: ΔE = hv
● Greater the energy, greater the frequency
● Smaller the wavelength, greater the energy
Example: determine the energy, in joules per photon, of radiation of frequency 7.38 x
10^15 Hz.
ΔE = hv
= (6.626 x 10^-34 Js) (7.38 x 10^15 s-1)
= 4.9 x 10^-18 J
, Velocity: Ephoton = ɸ + KE or hv = hv0 + ½mu2
ɸ = threshold energy
hv = incident photon
m = mass of electron
u = speed of electron
KE = kinetic energy
hv0 = threshold frequency (required)
Example: the minimum energy required to cause the photoelectric effect in
potassium metal is 3.69 x 10^-19 J. If 420 nm radiation is shone on potassium will
electrons be ejected? If yes, what is their velocity?
h= 6.626 x 10^-34 Js 1 nm = 1 x 10-9 m
me = 9.109 x 10^-31 kg 420 nm = 4.2 x 10-7 m
c= 2.9979 x 108 ms-1 ΔE = hv = hc/λ = (6.626 x 10^-34 Js) (2.9979 x 108 ms-1)
/
ɸ = 3.69 x 10^-19 J (4.2 x 10-7 m)
= 4.7 x 10^-19 J --> since this is larger than ɸ, photons will be ejected
Velocity: Ephoton = ɸ + KE
4.7 x 10^-19 J = 3.69 x 10^-19 J + ½ (9.109 x 10^-31 kg) u2
1.01 x 10^-19 J = (4.5545 x 10^-31 kg) u2
2.217 x 10^11 J/kg = u2
4.8 x 10^5 m/s = u
4.4 - Atomic Spectra
Balmer Series
● 4 wavelengths only visible
λ W (cm-1)
Hα Red 6563 15234 n1 = 3
Hβ Green blue 4862 20565 n1 =
4
Hγ Blue 4342 23033 n1 = 5
Hδ Violet 4103 24374 n1 = 6
