wave-particle duality 1 : the beginnings of quantum mechanics

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Wave-Particle Duality 1: The Beginnings of Quantum Mechanics

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Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics. Define the relationship between quantum and photon . Describe how a produced line spectra relates to the Bohr diagram for a specific element. Additional KEY Terms Absorption SpectraThreshold energy. PHOTOELECTRIC EFFECT. - PowerPoint PPT Presentation

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Page 1: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Wave-Particle Duality 1:The Beginnings of Quantum Mechanics

Page 2: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

• Define the relationship between quantum and photon.

• Describe how a produced line spectra relates to the Bohr diagram for a specific element.

Additional KEY Terms

Absorption Spectra Threshold energy

Page 3: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

PHOTOELECTRIC EFFECT

Under certain conditions, shining light on a metal surface will eject electrons.

Electrons given enough energy (threshold energy) can escape the attraction of the nucleus

Building on Planck’s quantum idea, Einstein

tried to explain this phenomenon…

Page 4: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Problem 1: Only high frequency light (high energy) will eject electrons - acting as particle.

Only explained if thought of as particles in a collision

Page 5: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Problem 2:Only more intense light (higher amplitude) will eject more electrons - acting as wave.

Only explained if thought of as changing the “size” – amplitude of the wave

Page 6: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Einstein (1905) – EMR is a stream of tiny “packets” of quantized energy carried in particles called - photons.

A photon have no mass but carries a quantum of energy

Light is an electromagnetic WAVE, made of

PARTICLE-like photons of energy

Page 7: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Compton (1922) – first experiment to show particle and wave properties of EMR simultaneously.

Incoming x-rays lost energy and scattered in a way that can be explained with physics of collisions.

Page 8: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics
Page 9: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Bohr (1913) – proposed that spectral lines are light from excited electrons.• Restricting electrons to fixed orbits (n) of

different quantized energy levels

Energyn = -2.18 x 10-18 J x Z2/n2

His equations correctly predicted the structured spectral lines of Hydrogen…

• Created an equation for energy of an electron at each orbit

Page 10: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

1. Electron absorbs a photon of energy and jumps from ground state (its resting state) to a higher unstable energy level (excited state).

Free Atom

e−EMR

e−

Ground State

e−

Excited State

Ionization Absorption

EMR

nucleus

> Threshold Energy < Threshold Energy

2. Electron falls back to ground state – releasing the same photon of energy.

“unstable” is the KEY - electrons are attracted to the nucleus and can’t stay away for long

Page 11: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

ΔE = E higher-energy orbit - E lower-energy orbit

= Ephoton emitted = hf

The difference in energy requirements between orbits determines the “colour” of photon absorbed/released by

the electron

Page 12: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

3. Levels are discrete (like quanta) – No in-between.

4. Every jump/drop has a specific energy requirement - same transition, same photon.

Page 13: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

The size of the nucleus will affect electron position around the atom – and the energy requirements

Cl:

17 e-

Na:11 p+

11 e- 17 p+Each element has a unique line spectrum as each

element has a unique atomic configuration

Page 14: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

We only “see” those excited electrons that require and releasing energy in the visible spectrum

Page 15: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

Absorption spectrum – portion of visible light absorbed by an element – heating up.

Emission spectrum – portion of visible light emitted by that element – cooling down.

Notice energy absorbed is the same as energy released

Page 16: Wave-Particle Duality 1 : The Beginnings of Quantum Mechanics

CAN YOU / HAVE YOU? • Define the relationship between quantum, photon

and electron.

• Describe how a produced line spectra relates to the Bohr diagram for a specific element.

Additional KEY Terms

Absorption Spectra Threshold energy