Ken Rogers

Miami Killian

Electrons move about the nucleus in energy levels.

1st Energy Level

2nd Energy Level

3rd Energy Level

1st 2nd 3rd

nucleus

These energy levels surround the nucleus of the atom.

Energy level 3

When energy is added to an atom, it causes electrons to move further away from the nucleus where the

electrons have more energy. This step is called

energy level 2

energy level 1

absorption.

The electron absorbs energy and moves to a higher energy level.

Energy level 3

When the electron falls back down to a lower energy level, the electron loses the energy it previously absorbed.

energy level 2

energy level 1

It emits this energy in the form of a photon of light or radiant energy.

emission.This step (where the electron gives back its absorbed energy) is called

Electromagnetic waves are produced by the movement of electrons within the atom. These

waves are also called "electromagnetic radiation" because they radiate from the electrically charged particles. They travel through empty space as well

as through air and other substances.

Scientists have observed that electromagnetic radiation has a dual

"personality."

Besides acting like waves, it acts like a stream of particles (called "photons") that

have no mass.

The photons with the highest energy correspond to the shortest wavelengths.

Electromagnetic Radiation

Do you listen to the radio, watch TV, or use a microwave oven? All thesedevices make use of electromagnetic waves. Radio waves, microwaves,visible light, and x rays are all examples of electromagnetic waves that differfrom each other in wavelength.

a) longer wavelength b) shorter wavelength

Measuring wavelength. . . . the distance from peak to peak or trough to trough is one way scientists measure the length of a wave.

peak to peak

trough to trough

lambda

400 nm 700 nm

Visible

Radio

Microwave

IRUVX-Rays

Gamma Rays

Electromagnetic SpectrumElectromagnetic Spectrum

BuildingsGrains of

sugarProtozoans Bacteria Molecules Atoms Atomic nuclei

103 1 1 – 10-3 10-3 – 10-6 8x10-7-4x10-7 3x10-7- 10-8 10-8 – 10-12 10-12Wavelength in meters

About the size of:

Radio InfraredMicrowave Visible Ultraviolet X-Ray Gamma Ray

Electromagnetic Spectrum

wavelength, = the distance between similar parts of the waves

frequency (f or ) = the number of waves per second (also called Hertz or cycles per second)

as the wavelength gets smaller (more crowded together) the frequency (# of waves) gets larger.

Count the number of waves that go by.

8

3

The shorter the wavelength, the higher the frequency.

The greater the wavelength, the lower the frequency.

To see that relationship, watch as we race these two light waves pass the red line.

This is an inverse proportion which is equal to a constant.The equation is:

wavelength times frequency equals a constant or

f = c

the value of the constant, c is 3.00 x 108 m/s

and is the speed of light.

so, f = 3.00 x 108 m/s

Example:All FM radio stations broadcast in megaHertz (1 x 106 waves/s).Coast FM, 97.3 on the FM dial, broadcasts 97.3 megaHertz or97.3 x 106/s. What is the wavelength (distance between waves) for this frequency of radio waves?

f = c

f = 3.00 x 108 m/s

97.3 x 106/s = 3.00 x 108 m/s

3.00 x 108 m/s

97.3 x 106/s

= 3.08 m

The energy that a photon of light possesses is a function of (depends on) its frequency.

The more waves light has, the more energy it has.

The equation is:

Energy of light = h . f or E = h . f

where h (Planck’s constant) is 6.63 x 10-34 joule . s

Or, the higher the frequency, the higher the energy.

This is a direct proportion.

Example:

What is the energy of a single photon of X-ray which has a frequency of 2.00 x 1018/s?

E = h . f

E = 6.63 x 10-34 joule . s . f

E = 6.63 x 10-34 J . s . 2.00 x 1018/s

E= 1.33 x 10-15 J (per photon)

Bright line emission spectrum for hydrogen

Bright line emission spectrum for sodium

Link

Glass Prism

Hydrogen gas in glass tube

Emission spectrum of hydrogen