Wave-Particle Duality:The Beginnings of Quantum Mechanics

• Explain the basics of wave-particle duality.

• 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

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.

*Light is acting like a “particle” in this experiment – collision.

Only high frequency light (> 1.14 x 10 15 Hz) will eject electrons - acting as particle.

Can only explain it if you think of it using photons in a collision.

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

Can only explain it if you think of it as changing the size of the wave.

Einstein (1905) - electromagnetic radiation is a stream of tiny bundles of energy called photons.

Photons have no mass but carry a quantum of energy.

One photon can remove one electron.

Light is an electromagnetic wave, yet it contains particle-like photons of energy.

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.

Quantum Mechanical Model of the Atom

Bohr (1922) – restricting electrons to fixed orbits (n) with different quantized energy levels.

Created a math equation for energy of each orbit.

Equations correctly predicted the line colours of hydrogen spectra.

Energyn = -(2.18 x 10-18 J)/n2

1. Electron absorbs radiation and jumps fromground state (its resting state) to a higher unstable energy level (excited state).

2. Electron soon loses energy and drops back down to a lower energy level – emitting the absorbed EMR.

Free Atom

e−EMR

e−

Ground State

e−

Excited State

Ionization Absorption

EMR

nucleus

> Threshold Energy < Threshold Energy

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

= Ephoton emitted = hf

• Levels are discrete like quanta – no in between.

• Each jump/drop is associated with a specific frequency photon - same transition, same photon.

The size of nucleus will affect electron position around the atom – and the size of “jump” energy.

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.

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

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

CAN YOU / HAVE YOU? • Explain the basics of wave-particle duality.

• 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