Post on 04-Jan-2016
Part II. Waves & Particles
Ch. 5 - Electrons in Atoms
QuantizedQuantized Energy vs. Energy vs. ContinuousContinuous
EnergyEnergy QuantizedQuantized Energy comes in Energy comes in
discrete packagesdiscrete packages ExampleExample: second : second
hand on clock that hand on clock that “ticks”“ticks”
STAIRSSTAIRS
ContinuousContinuous Energy is flowingEnergy is flowing ExampleExample: second : second
hand on clock that hand on clock that moves continuouslymoves continuously
ESCALATORESCALATOR
Dual Nature of Light……. Particle or Wave
• Remember a quantum of energy is the amount of energy to move an electron from one energy level to another.
• Energy is quantized therefore light must be quantized.
• These smallest pieces, quanta, are called ……photons : particles of light
• BUT, Energy is also continuous. Therefore light which is continuous acts like a WAVE
ThereforeTherefore……….……….
LLiigghhtt transmits energy as a transmits energy as a particleparticle
AndAnd
LLiigghht t travels through space as travels through space as a a wavewave
Quantum Theory
Einstein (1905)
Concluded - light has properties of both waves and particles
“ wave - particle duality ”
Wave-Particle DualityWave-Particle DualityJJ Thomson won the Nobel prize for describing the electron as a particle.
His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The
electron is a
particle!
The electron is an energy
wave!
Wave-Particle DualityWave-Particle DualityJJ Thomson won the Nobel prize for
describing the electron as a particle.His son, George Thomson won the
Nobel prize for describing the wave-like nature of the electron.
The electron is a particle!The electron is an energy wave!
Wave-Particle DualityWave-Particle DualityJJ Thomson won the Nobel prize for describing the electron as a particle.
His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron.
The electron
is a particle!
The electron is an energy
wave!
LLIIGGHHTT
A. Waves
Wavelength () - length of one complete wave
Frequency () - # of waves that pass a point during a certain time period hertz (Hz) = 1/s or s-1
Amplitude (A) - distance from the origin to the trough or crest
Parts of a wave
Wavelength
AmplitudeOrigin
Crest
Trough
High point
Low point
baseline of wave
Wavelength – distance from crest to crest
symbol: λ = “lambda”Amplitude – height of wave from the
origin to the peak; brightness, intensity of light
• Frequency – how frequently a way oscillates up & down; the # of times a wave completes a cycle of up & down motion
– Symbol is ν = “nu”– SI unit is Hertz (Hz) or cycles/sec (1s or
s-1)
Summary of LightSummary of Light
c =
E = hTherefore: energy is directly proportional to the frequency.
High frequency = high energy
Low frequency = low energy
Therefore: wavelength and frequency are indirectly proportional.
Short wavelength = high frequency
Long wavelength = low frequency
E = h
Energy of a wave – E (measured in joules)
Planck’s Constant 6.626 x 10-34 j*s
Frequency
c =
Speed of Light – 3 x 108 m/s
Wavelength
Frequency
Electromagnetic RadiationElectromagnetic Radiation ““LightLight””
The study of light led to the The study of light led to the development of the quantum development of the quantum mechanical model.mechanical model.
Light is a type of electromagnetic Light is a type of electromagnetic radiation.radiation.
Electromagnetic radiation includes Electromagnetic radiation includes many kinds of waves many kinds of waves
All light waves move at All light waves move at 3.00 x 103.00 x 1088 m/s m/s (c =the Speed of Light)
Relationship between Frequency & Wavelength
As Wavelength INCREASES, frequency ________________
As Wavelength DECREASES, frequency _______________
DECREASES
INCREASES
B. EM Spectrum
LOW
ENERGY
HIGH
ENERGY
B. EM Spectrum
LOW
ENERGY
HIGH
ENERGY
R O Y G. B I V
red orange yellow green blue indigo violet
B. EM Spectrum
Frequency & wavelength are inversely proportional
c = c: speed of light (3.00 108 m/s): wavelength (m, nm, etc.): frequency (Hz, 1/s or s-1)
B. EM Spectrum
GIVEN:
= ?
= 434 nm = 4.34 10-7 m
c = 3.00 108 m/s
WORK: = c
= 3.00 108 m/s 4.34 10-7 m
= 6.91 1014 s-1
EX: Find the frequency of a photon with a wavelength of 434 nm.
C. Quantum Theory
E: energy (J, joules)h: Planck’s constant (6.6262 10-34 J·s): frequency (s-1)
E = h
The energy of a photon is proportional to its frequency.
C. Quantum Theory
GIVEN:
E = ? = 4.57 1014 s-1
h = 6.6262 10-34 J·s
WORK:
E = h
E = (6.6262 10-34 J·s)(4.57 1014 s-1)
E = 3.03 10-19 J
EX: Find the energy of a red photon with a frequency of 4.57 1014 s-1.
Quantum Theory
Planck (1900)
vs.
Classical Theory Quantum Theory