I

II

III

Suggested Reading

Pages 97 - 103

Section 4-1

Radiant Energy

Light has characteristics of both waves and particles

Dual Nature of Light

Light – electromagnetic radiationAmplitudeWavelengthFrequencySpeed

Properties of Light,Wave Description of Light

Height of the wave Measures brightness

Amplitude

Distance between crests Visible light:

400nm (violet) – 750 nm (red)

Wavelength

All light moves through space at 3.00 x 108 meters per second.

Speed

The number of complete waves passing a fixed point in a given time.

Frequency =

=

Frequency

Speed of LightWavelength

C___

Visible Light

Red – longest Orange Yellow Green Blue Indigo Violet - shortest

Electromagnetic Spectrum

Heat Lamp

Short Wavelength = High frequency = High energy

Long Wavelength = Low frequency = Low Energy

Electromagnetic Spectrum

Photoelectric Effect

Electromagnetic Radiation strikes the surface of a metal, ejecting electrons. The flow of electrons creates an electric current.

Light consists of quanta of energy that behave like tiny particles.

Energy quanta = photons.

Photoelectric Effect Analogy

Coins in … nothing happens until the correct amount is reached. Then a drink is ejected.

Like energy in … nothing happens until the THRESHOLD FREQUENCY is reached. Then an electron is ejected.

Planck’s Theory

Energy exists in quanta.

Quantum: a small, specific amount of energy that can be gained or lost by an atom.

Plural = quanta

Planck’s Theory E = h E = quantum of energy in joulesh = Planck’s constant (6.626 x 10-34 j.s) = frequency of light in Hz or s-1

Put it all together:

Using Einstein’s Theory of Relativity formula: E = mc2

And Planck’s formula: Ephoton = hWe are able to calculate the apparent mass of a photon.

Bohr Model of the H-Atom - 1913

Electrons can exist in one of only a certain number of allowed orbits

Electron’s energy is higher when it is in orbits that are farther from the nucleus.

Energy Levels

Electrons in the (ground state) absorb a quantum of energy, jumps to a higher level. (Excited State)

Jumps down to a lower level, releases a quantum of energy, which corresponds to a certain wavelength of light.

Energy Levels

Each line represents a certain energy level jump.

Energy Levels Analogy

Energy Levels are like rungs on a ladder

You can’t stand in mid-air.

Electrons can’t exist in between levels.

Bohr’s Model

Only worked for Hydrogen.

Does not work for atoms with more than one electron.

Line Spectra – “Atomic Fingerprints”

Contain only certain colors or wavelengths.

Different from continuous spectrum.

Atomic emission spectrum.

What is Light – 2 min review