ELECTRONS AND WAVES

“No familiar conceptions can be woven around the electron. Something unknown is

doing we don’t know what.”

-SIR ARTHUR EDDINGTON

The Dilemma

Particles have mass and a specific position in space (matter)

Waves have NO mass and NO specific position in space (light and energy)

Is the electron a wave or particle?

Wave-Particle DualitySeveral disputes over whether or not light and the electron were waves or particles.

JJ Thomson won the Nobel prize for describing the electron as a particle.

George Thomson (JJ Thomson’s son) won the Nobel prize for describing the electron as a wave.

The electron is a particle!

The Wave Like Electron

Louis deBroglie

The electron propagates through space as an energy wave. To understand the atom,

one must understand the behavior of electromagnetic waves.

Types of Waves

Light Waves- vibrations of photons

Sound Waves-vibrations of air molecules and atoms

Water waves-vibrations of water molecules

Parts of a wave

Crest: Top of the Wave

Trough: Bottom of the Wave

Wavelength: the shortest distance between equivalent points on a continuous wave (crest to crest/trough to trough) typically measured in meters

Frequency: the number of waves that pass a given point per second. Hertz (Hz) is the SI unit.

Amplitude: the wave’s height from the origin to a crest, or from the origin to a trough. (Not affected by wavelength and frequency)

Electromagnetic SpectrumA spectrum that includes all forms of electromagnetic

radiation, with

the only difference

in the types of

Radiation being

their frequencies

and wavelengths.

ROYGBIV

The wave equation:

This speed is constant for all electromagnetic waves inside a vacuum (space)

Notice:

1. As frequency increases, wavelength decreases (inverse relationship)

2. As frequency increases, energy of the wave increases

Practice: What is the frequency of an X-ray with a wavelength of 1.15 x 10-10 m?

Give it another try:

1. What is the frequency of a water wave that has a wavelength of 5.87m with a speed of 34.2m/s?

2. If a radio wave has a frequency of 8.97 x 107 Hz, what is the wavelength of the wave?

Warm Up

A sound wave traveling at 350 m/s has a frequency of 500 Hz. What is its wavelength?

Is light a particle or wave? Light as a wave failed to explain:

1. Why heated objects emit only certain frequencies of light

The colors produced correspond with different wavelengths and frequencies.

2. Why some metals emit electrons when light at a given temperature shines on them (photoelectric effect)

Max Plank (1858-1947)

While studying the radiation emitted by solid bodies heated, known as black body radiation, he discovered that some how light and matter had to mingle.

Plank’s Theory (1900)

There is a fundamental restriction on the amount of energy that an object emits or absorbsMatter can either gain or lose energy but only in

small specific amounts called quantaQuantum- is the minimum amount of energy

that can be gained or lost by an atom.○ E= h x ʋ

E – energyʋ - frequencyh – Plank’s Constant (6.6262 x 10-34 J/s)

Plank’s Theory (1900)

Think of the dots as stepping stones:Each energy level is a stepping stoneElectron transitions involve jumps of a definite amount

of energyEach transition produces bands of light with definite

wavelengths. (Specific color) As an excited electron returns to the ground state they

emit energy, that appears as specific colors of the specific energy levels.

Photoelectric Effect: Some metals will eject electrons from their surface

when light of a certain frequency (or higher) hits their surface.

Solar Power

Albert Einstein

Duality of Light: Light can be both a wave and a particle

Proposed that light consist of quanta of energy that behave like tiny particles (photons)

Photons- a massless particle that carries a quantum of energy. This energy depends of the frequency of the photons.

Neils Bohr (1913)

Studied the hydrogen atom

determined that the atom only had certain allowable energy states

Ground State - lowest possible energy state

Excited State - when the atom absorbs energy

Neils Bohr Bohr suggested that the electrons

around the hydrogen atom could only be allowed in certain circular orbits around the nucleus

The smaller the electron’s orbit, the lower the atom’s energy state or energy level

The larger the electron’s orbit the higher the atom's energy level

Quantum Number: the number Bohr gave to each orbital around the atom

Energy State Ground State for hydrogen is 1s1 (n=1)

Meaning H has a single electron in the first energy levelH does not give off energy in the ground state

When energy is added, a single electron moves up to a higher energy level creating an excited atom The electron will fall back into its original quantum level

(ground state) and release the energy it gained as a photon (color)

Only specific frequencies are emitted by an atom Quantum's only allow a certain amount of energy to be

absorbed and emitted by the atom

Atomic Emission Spectrum Electrons absorb energy, jumping up to a different energy

level, and release the same amount of energy when falling back to the ground stateWhen the electrons falls back to the ground state is when it

releases the photon, a specific color is then seen.

The amount of energy has a specific frequency, that is visible in colorsThe color is the photons being released, and they are within the

visible light of the electromagnetic spectrum

Atoms absorb then release energy in the form of lightEvery element emits light containing only certain wavelengthsEach element has a very specific range of colors that are emitted.

Wave-Particle Duality

Louise de Broglie (1924)

Thought that if light can have both wave and particle properties/characteristics, then so could matter (electrons)

Predicted that all moving particles have wave-like characteristics

Werner Heisenberg (1901-1976)

Stated that it is impossible to take any measurement of an object without disturbing the object

Heisenberg Uncertainty Principal: states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time

*Meaning that Bohr’s defined orbits were not

accurate

Erwin Schrodinger (1926)

Quantum Mechanical model of the atom: the atomic model in which electrons are treated as waves This allowed scientist to determine particular

volumes of space around the nucleus in which the probability of finding an electron is very high

Atomic Orbital:

the probable location

of an electron within the atom

Answering the Dilemma of the Atom

Treat the electron as waves

As the electron moves away from the nucleus, the wavelength shortens

Shorter wavelengths = higher energy

Higher energy = greater distance from the nucleus