1. Chapter 5 in your textbook pp. 117-141
Electrons in atoms
Chapter 5 in your textbook pp

2. 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

3. 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

4. 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

5. Waves All waves can be described by several characteristics:
Wavelength
Frequency
Amplitude
Speed

6. 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

7. 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

8. Wave
Amplitude
Wave’s height from the origin to a crest, or from the origin to a trough

9. 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

10. 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

11. 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

12. 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)
The spectrum is called continuous because there is no portion of it that does not correspond to a unique wavelength and frequency of light.

13. 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

14. Electromagnetic Spectrum
Violet light has the greatest frequency and has more energy that the red light

15. 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 MHz. What is the wavelength of the broadcast? (1MHz = 106 Hz)

16. 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
A piece of iron appears dart gray at room temp, glows red when heated, and appears bluish in color at even higher temps. As iron gets hotter it has more energy and emits different colors of light.

17. 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

18. 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

19. 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

20. Question??