1. Chapter 7 The Quantum-Mechanical Model of the Atom

2. A Theory that Explains Electron Behavior
the quantum-mechanical model explains the manner electrons exist and behave in atoms
helps us understand and predict the properties of atoms that are directly related to the behavior of the electrons
why some elements are metals while others are nonmetals
why some elements gain 1 electron when forming an anion, while others gain 2
why some elements are very reactive while others are practically inert
and other Periodic patterns we see in the properties of the elements

3. The Nature of Light its Wave Nature
light is a form of electromagnetic radiation
composed of perpendicular oscillating waves, one for the electric field and one for the magnetic field
an electric field is a region where an electrically charged particle experiences a force
a magnetic field is a region where an magnetized particle experiences a force
all electromagnetic waves move through space at the same, constant speed
3.00 x 108 m/s in a vacuum = the speed of light, c

4. Electromagnetic Radiation

5. Characterizing Waves the amplitude is the height of the wave
the distance from node to crest
or node to trough
the amplitude is a measure of how intense the light is – the larger the amplitude, the brighter the light
the wavelength, (l) is a measure of the distance covered by the wave
the distance from one crest to the next
or the distance from one trough to the next, or the distance between alternate nodes

6. Characterizing Waves
the frequency, (n) is the number of waves that pass a point in a given period of time
the number of waves = number of cycles
units are hertz, (Hz) or cycles/s = s-1
1 Hz = 1 s-1
the total energy is proportional to the amplitude and frequency of the waves
the larger the wave amplitude, the more force it has
the more frequently the waves strike, the more total force there is

7. The Relationship Between Wavelength and Frequency
for waves traveling at the same speed, the shorter the wavelength, the more frequently they pass
this means that the wavelength and frequency of electromagnetic waves are inversely proportional
since the speed of light is constant, if we know wavelength we can find the frequency, and visa versa

8. Examples
Calculate the wavelength of red light with a frequency of 4.62 x 1014 s-1
Calculate the wavelength of a radio signal with a frequency of MHz

9. Color the color of light is determined by its wavelength or frequency
white light is a mixture of all the colors of visible light
a spectrum
RedOrangeYellowGreenBlueViolet
when an object absorbs some of the wavelengths of white light while reflecting others, it appears colored
the observed color is predominantly the colors reflected

10. Electromagnetic Spectrum
Tro, Chemistry: A Molecular Approach

11. Amplitude & Wavelength

12. The Electromagnetic Spectrum
visible light comprises only a small fraction of all the wavelengths of light – called the electromagnetic spectrum
short wavelength (high frequency) light has high energy
radiowave light has the lowest energy
gamma ray light has the highest energy
high energy electromagnetic radiation can potentially damage biological molecules
ionizing radiation

13. Thermal Imaging using Infrared Light
Using High Energy Radiation to Kill Cancer Cells

14. Interference the interaction between waves is called interference
when waves interact so that they add to make a larger wave it is called constructive interference
waves are in-phase
when waves interact so they cancel each other it is called destructive interference
waves are out-of-phase

15. Diffraction
when traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it – this is called diffraction
traveling particles do not diffract
the diffraction of light through two slits separated by a distance comparable to the wavelength results in an interference pattern of the diffracted waves
an interference pattern is a characteristic of all light waves

16. 2-Slit Interference

17. The Photoelectric Effect
it was observed that many metals emit electrons when a light shines on their surface
this is called the Photoelectric Effect
classic wave theory attributed this effect to the light energy being transferred to the electron
according to this theory, if the wavelength of light is made shorter, or the light waves intensity made brighter, more electrons should be ejected

18. The Photoelectric Effect The Problem
in experiments with the photoelectric effect, it was observed that there was a maximum wavelength for electrons to be emitted
called the threshold frequency
regardless of the intensity
it was also observed that high frequency light with a dim source caused electron emission without any lag time
analogy of the effect of throwing a thousand ping-pong balls at a window versus 1 baseball.

19. Particlelike Properties of Electromagnetic Energy
Chapter 5: Periodicity and Atomic Structure
Particlelike Properties of Electromagnetic Energy
4/22/2017
The book uses a nice analogy of the effect of throwing a thousand ping-pong balls at a window versus 1 baseball.
Copyright © 2008 Pearson Prentice Hall, Inc.

20. Einstein’s Explanation
Einstein proposed that the light energy was delivered to the atoms in packets, called quanta or photons
the energy of a photon of light was directly proportional to its frequency
inversely proportional to it wavelength
the proportionality constant is called Planck’s Constant, (h) and has the value x J∙s

21. Examples
Calculate the number of photons in a laser pulse with wavelength 337 nm and total energy 3.83 mJ
What is the frequency of radiation required to supply 1.0 x 102 J of energy from 8.5 x 1027 photons?
What is the energy (in kJ/mol) of photons of radar waves with ν = 3.35 x 108 Hz?
What is the energy (in kJ/mol) of photons of an X-ray with λ = 3.44 x m?

22. Kinetic Energy = Ephoton – Ebinding
Ejected Electrons
1 photon at the threshold frequency has just enough energy for an electron to escape the atom
binding energy, f
for higher frequencies, the electron absorbs more energy than is necessary to escape
this excess energy becomes kinetic energy of the ejected electron
Kinetic Energy = Ephoton – Ebinding
KE = hn - f

23. Spectra
when atoms or molecules absorb energy, that energy is often released as light energy
fireworks, neon lights, etc.
when that light is passed through a prism, a pattern is seen that is unique to that type of atom or molecule – the pattern is called an emission spectrum
non-continuous
can be used to identify the material
Rydberg analyzed the spectrum of hydrogen and found that it could be described with an equation that involved an inverse square of integers

24. Examples of Spectra
Oxygen spectrum
Neon spectrum

25. Emission vs. Absorption Spectra
Spectra of Mercury

26. Bohr’s Model
Neils Bohr proposed that the electrons could only have very specific amounts of energy
fixed amounts = quantized
the electrons traveled in orbits that were a fixed distance from the nucleus
stationary states
therefore the energy of the electron was proportional the distance the orbital was from the nucleus
electrons emitted radiation when they “jumped” from an orbit with higher energy down to an orbit with lower energy
the distance between the orbits determined the energy of the photon of light produced

27. Bohr Model of H Atoms

28. Wavelike Properties of Matter
Chapter 5: Periodicity and Atomic Structure
Wavelike Properties of Matter
4/22/2017
Louis de Broglie in 1924 suggested that, if light can behave in some respects like matter, then perhaps matter can behave in some respects like light.
In other words, perhaps matter is wavelike as well as particlelike. mv h
l =
The de Broglie equation allows the calculation of a “wavelength” of an electron or of any particle or object of mass m and velocity v.
Copyright © 2008 Pearson Prentice Hall, Inc.

29. Examples
What is the de Broglie wavelength (in meters) of a small car with a mass of kg traveling at a speed of 55.0 mi/h (24.6 m/s)?
What velocity would an electron (mass = 9.11 x 10-31kg) need for its de Broglie wavelength to be that of red light (750 nm)?

30. examples
What velocity would an electron (mass = 9.11 x 10-31kg) need for its de Broglie wavelength to be that of red light (750 nm)?
What is the velocity of an electron having a de Broglie wavelength that is approximately the length of a chemical bond? Assume this length to be 1.2 x m
Determine the wavelength of a neutron traveling at 1.00 x 102 m/s (Massneutron = x g)

31. Quantum Mechanics and the Heisenberg Uncertainty Principle
Heisenberg Uncertainty Principle – both the position (Δx) and the momentum (Δmv) of an electron cannot be known beyond a certain level of precision
1. (Δx) (Δmv) > h 4π
2. Cannot know both the position and the momentum of an electron with a high degree of certainty
3. If the momentum is known with a high degree of certainty
i. Δmv is small
ii. Δ x (position of the electron) is large
4. If the exact position of the electron is known
i. Δmv is large
ii. Δ x (position of the electron) is small

32. Determinacy vs. Indeterminacy
according to classical physics, particles move in a path determined by the particle’s velocity, position, and forces acting on it
determinacy = definite, predictable future
because we cannot know both the position and velocity of an electron, we cannot predict the path it will follow
indeterminacy = indefinite future, can only predict probability
the best we can do is to describe the probability an electron will be found in a particular region using statistical functions