Chapter 5 in your textbookpp. 117-141

Wave Nature of Light

In the early 1900s scientists observed that certain elements emitted visible light when heated in a flame

Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electron’s in its atoms

Wave Nature of Light

For you to better understand the

relationship and the nature of atomic

structure, you need to understand

the nature of light

Wave Nature of Light

Electromagnetic radiation A form of energy that exhibits wavelike

behavior as it travel through space

Visible light is a type of electromagnetic radiation

Examples include: visible light from the sun, microwaves, x-rays, radio waves

Waves

All waves can be described by several characteristics:

Wavelength Frequency Amplitude Speed

Wave

Wavelength (λ) Shortest distance between equivalents

points on a continuous wave Measured from crest to crest or from

through to through Units: meters, centimeters, nanometers

Wave

Frequency (ν) Number of waves that pass a given point

per second

Unit: Hertz (Hz) = one wave per second (1/s) or (s-1)

Example : 652 Hz = 652 waves/second=652/s = 652 s-1

Wave

Amplitude Wave’s height from the origin to a

crest, or from the origin to a trough

Wave

All electromagentic waves, including visible light, travel at a speed of 3.00 x 108 m/s

c = λν c = speed of light, λ = wavelength, ν = frequency

The seed of light is the product of its wavelength and its frequency

Example

What is the wavelength of a microwave with a frequency of 3.44 x 109 Hz?

c = λν λ = c / ν

λ = 3.00 x 108 m/s =

3.44 x 109 s-1

8.72 x 10-2 m

Electromagnetic Spectrum

Although the speed of all electromagetic waves is the same, waves may have different wavelengths and frequencies

Wavelength and frequency are inversely related

As one quantity increase the other decrease

Electromagentic Spectrum

White light, such as sunlight, can be separated into a continuous spectrum of colors if passed through a prism

These are the colors of the rainbow (roy g biv) – red, orange, yellow, green, blue, indigo, violet)

Electromagnetic Spectrum

Electromagnetic spectrum (EM spectrum) is:

all forms of electromagnetic radiation

the only difference in the types of radiation is their wavelengths and frequencies

Each color has a different wavelength- Red has the longest wavelength and violet has the shortest wavelength

Electromagnetic Spectrum

Violet light has the greatest frequency and has more energy that the red light

Practice Problems What is the frequency of green light, which has a

wavelength of 4.90 x 10-7 m?

An X-ray has a wavelength of 1.15 x 10-10m. What is its frequency?

What is the speed of an electromagetic wave that has a frequency of 7.8 x 106 Hz?

A popular radio station broadcasts with a frequency of 94.7 MHz. What is the wavelength of the broadcast? (1MHz = 106 Hz)

Why we care about spectroscopy? Quantum concept: the temperature

of an object is a measure of the average kinetic energy in particles.

Different forms of matter will emit and absorb light at characteristic wavelengths and frequencies

Spectroscopy

The study of how (and at what wavelengths) a sample emits and/or absorbs light is a way to:

Identify components in a sample (ex: elements & molecules)

Quantify concentration of these components

Identify types of bonds in a molecule

Emission Spectroscopy

Flame emission spectroscopy

Atoms absorb energy in a flame and then emit energy as light

The wavelengths of emitted light are characteristics to individual atoms

The intensity of emitted light is proportional to the element’s concentration

Emission Spectroscopy continued The origin of this emission is the Decay,

Relaxation, Excited of electrons from a high energy state to a more stable lower energy state

The wavelength of emitted light corresponds to the energy difference between these two states

Question??