5.1 THE NATURE OF LIGHTChemistry

Ms. Pollock

2013 - 2014

INTRODUCTION

Understanding of Rutherford’s model requires understanding of light

1600s debate about how light travels Isaac Newton – light beam of particles Christian Huygens – light wave of energy

Neither hypothesis dominant until 1864 wave model of light (James Clerk Maxwell) accepted by many Relationship between magnetism and electricity Debate renewed by Max Planck sixty years later

INTRODUCTION

Above left: Newton;

above right: Huygens;

below left: Planck;

below right: Maxwell

THE WAVE FORM OF ENERGY

Wave model of electromagnetic radiation similar to waves on rope

Moving rope up and down with one end secured, motion passed from one part of rope to next

Rope gains wave shape

THE WAVE FORM OF ENERGY

Crest – highest point of wave

Trough – lowest point of wave

No horizontal motion of particles

Wavelength – distance from one crest to the next crest; symbol

THE WAVE FORM OF ENERGY

Amplitude – maximum height of wave

Velocity – distance traveled by wave in one second (unit m/s, symbol )

Frequency – number of cycles that pass a given point per unit of time (unit 1/s or s-1)

Hertz – wave cycles per second (symbol )

THE WAVE FORM OF ENERGY

Velocity, wavelength and frequency related = Velocity = frequency X wavelength What is the wavelength of a water wave if its

velocity is 5.0 m/s and its frequency is 2.0 s-

1? = = 5.0 m/s = 2.5 meters 2.0 s-1

ELECTROMAGNETIC WAVES

Form of electromagnetic radiation with electric and magnetic fields moving at the speed of light

Carry energy from one place to another and are like waves on rope

Do not require medium Energy traveling in straight line along path of

wave Associated oscillating electrical field and

oscillating magnetic field

ELECTROMAGNETIC WAVES

ELECTROMAGNETIC WAVES

Light waves still characterized by wavelength, frequency, and velocity

Velocity of all electromagnetic waves in vacuum same value (3.00 X 108 m/s), symbolized by c

c = What is the wavelength of an

electromagnetic wave traveling in air whose frequency is 1.00 X 10 14 s-1?

= c = 3.00 X 108 m/s = 3.00 X 10-6 m 1.00 X 1014 s-1

THE ELECTROMAGNETIC SPECTRUM

Frequency related to energy and amplitude of electromagnetic waves

Frequency able to be converted to energy by multiplying by Planck’s constant (h = 6.6 X 10-34Js)

E = h Wide range of frequencies, wavelengths, and

energies in spectrum Electromagnetic spectrum – range of all

possibilities of electromagnetic radiation

THE ELECTROMAGNETIC SPECTRUM