Chapter Summary/Important Vocab

• Waves and Light

• Quantum Theory

• Electromagnetic Spectrum

• Atomic Emission Spectrums

Components of a Wave

Low & High Frequency Waves:

The formula

c = hv

• c = Speed of Light (3 × 10^8 m/s)

• h = Wavelength (m)

• v = Frequency ( s^-1 or Hz)

Quantum Theory and Planck

Max Planck 1900

• Hypothesized that the energy radiated from a heated object, such as a stove element or a lightbulb filament, is emitted in discrete units quanta.

• As energy increases, so does intensity.

Planck

E = hv

• E = Energy per Quantum (J)

• h = Planck’s Constant (6.63 × 10^-34 Js)

• v = Frequency (s^-1)

The Photoelectric Effect

• The science world knew that certain clean metal surfaces would shed electrons when certain frequencies of light were shined on them.

• 1st Fact: Highly intense low frequency light does not eject any electrons, even if it shines on the surface for several days.

• 2nd Fact: When the threshold frequency is reached, electrons are ejected immediately.

• 3rd Fact: increasing the Intensity of the Light at a frequency that will cause electrons to eject results at a higher ejection rate. However, all ejected electrons share the same velocity.

• 4th: Increasing the frequency of the light increases the velocity of the ejected electrons. However

• , all ejected electrons share the same velocity.

Einstein’s Theory (1905)

• A Beam of light is a stream of particles called photons.

• The energy of a photon is related to its frequency according to E = hv.

• The quantum of Planck is a particle - a photon.

• If the frequency of a photon is below a certain threshold, no electrons are ejected.

• If the frequency of the photon is or above a certain threshold, its energy is transferred to the electron.

Planck and Einstein

E = hv

• E = Energy per Photon (J)

• h = Planck’s

• Constant (6.63 × 10^-34 Js)

• v = Frequency (s^-1)

The Electromagnetic Spectrum is a Continuous Spectrum of Light

Atomic Emission Spectrum

Why do we have different colors of Light?

• As wavelength frequency changes, color changes.

• But there is a duality to light:

  • It behaves like a wave, and

  • It behaves like a particle (A photon)

• As wavelength/frequency changes, the energy per photon changes.

  • E = hv

Absorbing Photons

• When a photon is absorbed by an atom or molecules, an electron moves up one or more energy levels.

• The increase in energy is equal to the energy of the photon that was absorbed.

• The increase in energy is also equal to the difference in energy between the two energy levels.

Emitting Photons

• When a photon is emitted from an atom or molecule, an electron moves down one or more energy levels..

• The decreases in energy is equal to the energy of the photon that was released.

• The decrease in energy is also equal to the difference between the two energy levels.