Part II. Waves & Particles Ch. 5 - Electrons in Atoms

Quantized Energy vs. Continuous Energy Quantized Quantized Energy comes in discrete packages Energy comes in discrete packages Example: second hand on clock that “ticks” Example: second hand on clock that “ticks” STAIRS STAIRS Continuous Continuous Energy is flowing Energy is flowing Example: second hand on clock that moves continuously Example: second hand on clock that moves continuously ESCALATOR ESCALATOR

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

Therefore………. Light transmits energy as a particle And Light travels through space as a wave

Quantum Theory Einstein (1905) Concluded - light has properties of both waves and particles “ wave - particle duality ”

Wave-Particle Duality JJ 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!

zWave-Particle Duality zJJ Thomson won the Nobel prize for describing the electron as a particle. zHis son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. zThe electron is a particle! zThe electron is an energy wave!

Wave-Particle Duality JJ 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!

LIGHTLIGHTLIGHTLIGHT

A. Waves zWavelength ( ) - length of one complete wave zFrequency ( ) - # of waves that pass a point during a certain time period yhertz (Hz) = 1/s or s -1 zAmplitude (A) - distance from the origin to the trough or crest

Parts of a wave Wavelength Amplitude Origin 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 Light c = E = h Therefore: 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 x j*s Frequency

c = Speed of Light – 3 x 10 8 m/s Wavelength Frequency

Electromagnetic Radiation “ Light ” The study of light led to the development of the quantum mechanical model. The study of light led to the development of the quantum mechanical model. Light is a type of electromagnetic radiation. Light is a type of electromagnetic radiation. Electromagnetic radiation includes many kinds of waves Electromagnetic radiation includes many kinds of waves All light waves move at 3.00 x 10 8 m/s All light waves move at 3.00 x 10 8 m/s (c =the Speed of Light)

Relationship between Frequency & Wavelength As Wavelength INCREASES, frequency ________________ As Wavelength DECREASES, frequency _______________ DECREASES INCREASES

B. EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY ROYG.BIV redorangeyellowgreenblueindigoviolet

B. EM Spectrum zFrequency & wavelength are inversely proportional c = c:speed of light (3.00  10 8 m/s) :wavelength (m, nm, etc.) :frequency (Hz, 1/s or s -1 )

B. EM Spectrum GIVEN: = ? = 434 nm = 4.34  m c = 3.00  10 8 m/s WORK : = c = 3.00  10 8 m/s 4.34  m = 6.91  s -1 zEX: Find the frequency of a photon with a wavelength of 434 nm.

C. Quantum Theory E:energy (J, joules) h:Planck’s constant (  J·s) :frequency (s -1 ) E = h zThe energy of a photon is proportional to its frequency.

C. Quantum Theory GIVEN: E = ? = 4.57  s -1 h =  J·s WORK : E = h E = (  J·s ) ( 4.57  s -1 ) E = 3.03  J zEX: Find the energy of a red photon with a frequency of 4.57  s -1.

Quantum Theory zPlanck (1900) vs. Classical TheoryQuantum Theory