1. 5.1 – ELECTRONS IN ATOMS

2. 5.1 WAVE NATURE OF LIGHT: Important in understanding electrons.
Electromagnetic radiation – Form of energy which includes visible light, microwaves, X-rays, radio waves, etc.

3. ELECTROMAGNETIC RADIATION TRAVELS IN WAVES
Wavelength () – distance between 2 waves
Units: m, cm, nm (1nm = 1 x 10-9 m)
Frequency () - # waves that pass a given point per second
Units: waves/sec, hertz (1 wav/s = 1 hz)
Amplitude - wave’s height
from origin (middle) to crest.

4. VELOCITY: All electromagnetic radiation travels at the speed of light, “c”.
c = 3.00 x 108 m/s
c = 
Wavelength & frequency: inversely proportional
If wavelength increases, frequency decreases.

5. c =  (solving for wavelength, , lambda)
PROBLEM: Find wavelength of a microwave having a frequency of 3.44 x 109 Hz?
c =  (solving for wavelength, , lambda)
c = 3.00 x 108 m/s (constant)
 = 3.44 x 109 Hz (s-1or per second)
Plug into equation:
3.00 x 108 m/s =  x x 109/s
3.00 x 108 m/s = 
3.44 x 109/s
 = 8.72 x 10-2 m

6. PROBLEM: Find the frequency of green light which has a wavelength of 4
PROBLEM: Find the frequency of green light which has a wavelength of 4.90 x 10-7 m.
c =  (solving for frequency, , nu)
c = 3.00 x 108 m/s (constant)
 = 4.90 x 10-7 m
Plug in:
3.00 x 108 m/s = 4.90 x 10-7 m x 
3.00 x 108 m/s = 
4.90 x 10-7 m
 = 6.12 x 1014s-1
(or Hertz)

7. WHITE LIGHT: Prism separates into a continuous spectrum -- ROYGBIV
Red light – lower frequency
(longer wavelength) than violet light.

8. QUIZ 1) Name 3 types electromagnetic radiation.
2) What is the velocity of all electromagnetic radiation?
3) The distance between waves is ____().
4) The number waves per second is ___().
5) The higher the frequency, the ___the wavelength.
6) A prism separates white light into the ___ spectrum.

9. ELECTROMAGNETIC RADIATION

10. Iron – dark gray at room temperature
PARTICLE NATURE OF LIGHT: Explains why heated objects emit specific frequencies of light.
Iron – dark gray at room temperature
red when hotter, bluish when v. hot.
(Photon of light)

11. MAX PLANCK (1900) – Quantum concept of energy:
Matter gains or loses energy in small specific amounts called quanta.
Quantum – minimum amount of energy that can be gained/lost by an atom.
Equation: E = h
Where: E = energy (joules)
h = Planck’s constant
6.626 x js
 = frequency

12. E = h Frequency & energy are directly proportional.
High frequency,
high energy
(small wavelength)
Energy:
In whole number multiples of h.
If energy decreases,
what happens to ?
How is  related to energy?

13. PROBLEM: Find energy of photon of violet light having frequency of 7
PROBLEM: Find energy of photon of violet light having frequency of 7.23 x 1014/sec.
E = h (E is unknown)
h = Planck’s constant
= x js
Plug in:
E = x js x 7.23 x 1014s-1
E = 4.79 x J (ans.) (joule)

14. Effect explained by Einstein (1905):
PHOTOELECTRIC EFFECT: Light shining on a metal’s surface results in emission of (photo) electrons.
Ex. Solar calculator – converts light into electrical energy
Effect explained by Einstein (1905):
Light has particle & wave nature.
Photons – stream of tiny particles of light.
Bundles of energy.
No mass.
Ephoton = h
(Planck)

15. ATOMIC EMISSION SPECTRA: Set of frequencies of electromagnetic waves emitted by atoms of an element.
Spectrum is unique for each element.
Ex. Sr atoms – Emit a characteristic red color.
Can use spectrum to identify an element.
Atomic spectrum consists of several individual lines of color
(Not continuous).

16. Elements emit a characteristic color.
When the element is heated, electron moves to higher energy level. (excited)
When electron returns to the ground state, a photon of light is emitted corresponding to the difference in energy.

18. QUIZ 1) Light has a wave nature and a ___nature.
2) According to Planck’s equation, the higher the frequency, the ___ the energy. This is ___ proportional.
3) The set of frequencies emitted by atoms of an element is called the atomic ____ _____.
4) In the flame tests, what causes the characteristic color of the element?

19. THE END