1. Chemistry Jacqueline P. Hancock, B.S. M.Ed
Quantum Theory Part 2
Chemistry
Jacqueline P. Hancock, B.S. M.Ed

2. Quantum Theory Allows us to predict and understand the role
e- play in chemistry
1. How many e- are in a particular atom??
2. What energies do individual e- possess?
3. Where in the atom are e- found?

3. Macroscopic View Molecules behave like rebounding balls
Does not explain the stability of atoms and the forces that hold them together
Properties of atoms are not governed by the same law as larger materials

4. Max Planck German physicist-(1858-1947)
1900 he discovered that atoms and molecules emit energy only in discrete quantities that he called quanta.
He did this while analyzing data on radiation emitted by solids heated to various temps.
Nobel Prize in Physics(1918) for Quantum Theory

5. What is a wave?
To understand Quantum Theory we must understand the nature of a wave…
Wave is a vibrating disturbance through which energy is transmitted.
2 Types of Waves
Transverse Wave
Longitudinal Wave

6. Transverse Waves
The medium moves at right angles to the direction the wave travels. The waves are traveling transverse or across the medium

7. Parts of a Transverse Wave

8. Longitudinal Waves
The medium is moved parallel to the direction that the waves are traveling.
Example: The coils in a spring move back and forth in the same direction as the wave travels

9. Parts of a Longitudinal Wave

10. Wavelength λ (lambda)- distance between identical points on successive waves......LENGTH
Frequency υ (nu) # of waves that pass a particular point in 1 second.
SI unit is the Hertz (Hz)
1 Hertz 1 Hz cycle/s 1/s

11. Amplitude- is the vertical distance from the midline of a wave to the peak or trough.

12. Wave speed formulas u = λ·υ c = λ·υ Where: υ =frequency λ=wavelength
u = speed of wave
Use with any wave other than electromagnetic radiation
c = λ·υ
Where:
υ =frequency
λ=wavelength
c = speed of light
c = 2.998x108m/s
Must use with EMR

14. Know your calculator!!!

18. Practice
Calculate the speed of a wave whose wavelength and frequency are 17.4 m and 87.4 Hz, respectively
λ = u = λ·υ
υ =
u =

19. Calculate the frequency in Hz of a wave whose speed and wavelength are 712m/s and 1.14m respectively.

20. Write Q & A –left side INB
Calculate the speed of a wave whose wavelength and frequency are 3.14x10-31 nm and 32.5x1018 Hz respectively. Calculate the frequency in Hz of a wave whose speed and wavelength are 7.12x1012m/s and 1.14x105m respectively.

21. Calculate the frequency in Hz of a wave whose speed and wavelength are 7.12x1012m/s and 1.14x105m respectively.

22. Electromagnetic Radiation
1873 James C. Maxwell proposed visible light consists of electromagnetic waves.
Maxwell's Theory--an electromagnetic wave has an electric field and magnetic field.
Provides mathematical description of behavior of light.

23. All EM waves travel at 2.998x108m/s
Electromagnetic Radiation is the emission of energy from electromagnetic waves
All EM waves travel at 2.998x108m/s
Approx. 186,000miles/s in a vacuum
299,800,000m/s
373m/s

24. ELECTROMAGNETIC WAVES
Transverse Wave made up of
electric fields and magnetic
fields that are oscillating at
90oangles
How do they travel?

25. Electromagnetic Spectrum all ER
in order of increasing frequency
ROY G BIV

26. EM Wave Calculations c = λ·υ Where: υ =frequency λ=wavelength
c = speed of light
c = 2.998x108m/s
Must use with EMR

27. The wavelength of the green light from a traffic signal is centered at 522 nm. What is the frequency of this radiation?

28. # 14. What is the wavelength of radiation with a frequency of 1
# 14.What is the wavelength of radiation with a frequency of 1.50 x 1013Hz? Does this radiation have a longer or shorter wavelength than red light?
#15. What is the frequency of radiation with a wavelength of 5.00x10-8m? In what region of the electromagnetic spectrum is this radiation?

29. Classical Atomic Theory
When you heat solids they will emit radiation over a wide range of wavelengths
We know this as:
Classical Theory
*Atoms and molecules admit or absorb any arbitrary amount of radiant energy.*
This was only good to explain short wavelengths and not long ones.

30. Planck’s Quantum Theory
Atoms and molecules emit or absorb only in discrete quantities like small packages or bundles called quanta.
Quantum= smallest quantity of energy that can be emitted or absorbed from EM radiation

32. In 1905 Einstein used the theory to solve the photoelectric effect.
* electrons are ejected from surface metals exposed to light of at least a certain minimal frequency.
Einstein assumed a beam of light behaved as a stream of particles called photons and said....
E=h•υ

33. E=h•υ c = λ·υ E=h• c λ E = energy of quantum of energy
h= Planck’s constant 6.63x10-34 J •s
υ = frequency of light
SI Units of quantum of energy is Joule (J)
c = λ·υ
E=h• c λ

34. Wave vs. Particle Electromagnetic waves are waves that
sometimes behave as a stream of particles.
How do we know?

35. Evidence of Wave Model
In 1801 Thomas Young passed a beam of light first through a single slit and then through a double slit. When the light reached a darkened screen there were alternating bright and dark bands
The bright bands= constructive interference
The dark bands= destructive interference

36. What did this mean? Interference only occurs with waves
Therefore light behaved like a wave.

37. Evidence of Particle Motion
1905 Albert Einstein determined that light behaved as packets of energy called photons
When the photons have enough energy(frequency) they can cause the release electrons(energy)
The greater the light frequency-the greater the energy released

38. Evidence of Particle Model
Photoelectric Effect is the emission of electrons from a metal caused by light striking the metal
Blue light has a higher frequency than red light so photons of blue light have more energy than photons of red light.
Red light will not cause the emission of electrons.

39. Photoelectric Effect

40. What does this mean?
Removing e requires a light of sufficiently high frequency(high energy) to break them free.
Shining a beam of light on a metal surface/shooting a beam of particles(photons) at the metal atoms.
If the frequency of photons(h•υ) is equal to the energy binding the e in the metal, then the light will have enough energy to knock e loose.
If (h•υ) hv is a higher frequency the e will also acquire kinetic energy

41. Heinsenberg Uncertainty Principle
Impossible to know exactly both the velocity and position of particle at the same time. Schrodinger combined this principle and wave properties to formulate his quantum description of e- in atoms

42. Atomic Emission Spectrum
Later 19 century we found that the amount of radiation energy emitted by an object at certain temperatures depends on its wavelength.
Frequencies of light emitted by an element corresponds to a particular “color” and separates in discrete lines.

46. Emission vs. Absorption

47. The energy of a photon is 5. 87x10-20J
The energy of a photon is 5.87x10-20J. What is it’s wavelength(in nanometers)?

48. Calculate the energy in joules of a photon with a wavelength of 5
Calculate the energy in joules of a photon with a wavelength of 5.00x104 nm (infrared region).

49. Calculate the energy in joules of a photon with a wavelength of 5 x10-2 nm (x ray region)