1. Last week's solar storms showered particles on the Earth that excited oxygen atoms high in the Earth's atmosphere. As the excited element's electrons fell back to their ground state, they emitted a red glow. Were oxygen atoms lower in Earth's atmosphere excited, the glow would be predominantly green.

2. Homework #2 due no later than Friday, February 3, 5:00 pm.
Answers to Homework #1 are now posted on the Homework page of the class website

3. Three Basic Types of Energy
kinetic
energy of motion
potential
stored energy; e.g., chemical, gravitational, electrical, etc.
radiative
energy transported by light (electromagetic radiation)

4. Is there a problem with perpetual motion machines?

5. Radiative energy: energy carried by electromagnetic radiation.
We will discuss electromagnetic radiation following a brief discussion of matter.

6. Atom
nucleus
electron p+ e- n
proton
neutron

7. Although it is the smallest part of the atom, most of the atom’s mass is contained in the nucleus.

8. Protons have a positive electrical charge
Electrons have a negative electrical charge
In a typical neutral atom, there are equal numbers of protons and electrons
The electrons do not “orbit” the nucleus; they are “smeared out” in a cloud which give the atom its size.

9. Incorrect view
better view

10. The particles in the nucleus determine the element & isotope.

11. Type of element is determined by #protons atomic number = #protons
Isotope of element is determined by # neutrons
atomic mass number = #protons + #neutrons

12. Different Elements (different # protons)
Hydrogen e-
Helium p+ p+ p+ n n e-
atomic number = 1
atomic number = 2
atomic mass number = 1
atomic mass number = 4

13. Atomic Number. Element. 1. Hydrogen (H). 2. Helium (He). 3
Atomic Number Element Hydrogen (H) Helium (He) Lithium (Li) Beryllium (Be) Boron (B) Carbon (C) Nitrogen (N) Oxygen (O) Each of these have multiple isotopes, some of which are not stable

14. Different Isotopes (same # protons, different # neutrons)1H 2H 3H p+ p+ p+ n n n
atomic number = 1
atomic mass number = 1
atomic number = 1
atomic mass number = 2
atomic number = 1
atomic mass number = 3

15. Some isotopes of an element may be stable, while other isotopes may be unstable (“Radioactive”) Unstable isotopes “decay”, producing a new type of atom, i.e., an atom of a different element.

16. Three isotopes of Carbon, two stable, one unstable.
Three isotopes of Hydrogen, two stable, one unstable. 1H 2H 3H
12.32yr %
0.0184%

17. One half of the atoms of an unstable isotope decay in one “half-life” of that isotope.

18. What if an electron is missing?
ion e- p+ p+ n n
atomic number = 2
He+1
atomic mass number = 4

19. What if two or more atoms combine to form a particle?
molecule p+ p+
8p+
Sharing of electrons (chemistry) is involved in the construction of molecules 8n
H2O (water)

20. ConceptTest
If you added a proton to an atom to create a new stable, isolated atom, you would have created
(blue) an isotope of the original element
(orange) a fission reaction
(red) a different element with a positive charge
(green) a neutron and a positron

21. ConceptTest
If you added a proton to an atom to create a new stable, isolated atom, you would have created
(blue) an isotope of the original element
(orange) a fission reaction
(red) a different element with a positive charge
(green) a neutron and a positron

22. Concept Test
If you removed an electron from an atom, you would have created
(blue) an isotope of the original element
(orange) a fission reaction
(red) a different element with a positive charge
(green) an ionized atom

23. Concept Test
If you removed an electron from an atom, you would have created
(blue) an isotope of the original element
(orange) a fission reaction
(red) a different element with a positive charge
(green) an ionized atom

24. Concept Test
Some nitrogen atoms have 7 neutrons and some have 8 neutrons. This makes these two forms of nitrogen
(yellow) ions of each other
(blue) isotopes of each other
(red) different elements
(green) phases of each other

25. Concept Test
Some nitrogen atoms have 7 neutrons and some have 8 neutrons. This makes these two forms of nitrogen
(yellow) ions of each other
(blue) isotopes of each other
(red) different elements
(green) phases of each other

26. Concept Test
If you combined two atoms such that they shared electrons to create a new stable object, you would have created
(blue) an isotope of the original element
(orange) a molecule
(red) a different element
(green) an ionized atom

27. Concept Test
If you combined two atoms such that they shared electrons to create a new stable object, you would have created
(blue) an isotope of the original element
(orange) a molecule
(red) a different element
(green) an ionized atom

28. Phases of Matter solid liquid gas plasma
the phases
solid
liquid
gas
plasma
depend on how tightly the atoms and/or molecules are bound to each other
As temperature increases, these bonds are loosened:

29. In thinking about phases of matter, recall that temperature measures the average kinetic energy of particles. Faster particles can escape electrical bonds easier.

30. Why does evaporation cool a liquid (consider perspiration)?

31. Radiative energy: energy carried by electromagnetic radiation (light).

32. Light Light as a wave Light as a particle (photon)
A vibration in an electromagnetic field
through which energy is transported.
Light as a wave
Light as a particle
(photon)

33. Properties of Waves WAVELENGTH (: Distance between adjacent crests
FREQUENCY (f): number of crests that pass through a point each second. It is measured in units of hertz (Hz), which are the number of cycles per second.
AMPLITUDE: A measure of the strength of the wave.
SPEED (s): how fast the wave pattern moves For any wave: s = f 

34. The speed of light is a constant: s = c !!!
Therefore, for light: f  = c
The higher f is, the smaller  is, and vice versa.
In the visible part of the spectrum, our eyes recognize f (or ) as color!

35. Light can also be treated as photons – packets of energy.
The energy carried by each photon depends on its frequency (color)
Energy: E = hf = hc/  [“h” is called Planck’s Constant]
Shorter wavelength light carries more energy per photon.

36. The Electromagnetic Spectrum
lower energy
higher energy

37. Light as Information Bearer
Spectrum: light separated into its different wavelengths.
Spectroscopy: The quantitative analysis of spectra
The spectrum of an object can reveal the object’s:
Composition
Temperature
Velocity

38. Got here

39. Four Ways in Which Light can Interact with Matter
emission – matter releases energy as light
absorption – matter takes energy from light
transmission – matter allows light to pass through it
reflection – matter repels light in another direction
The type of interaction is determined by characteristics of the “matter” and the wavelength of light.

40. Different wavelengths of light interact differently with the atmosphere

41. Three ways in which spectra manifest themselves:
Continuous spectra
Absorption spectra
Emission line spectra

42. Continuous spectra are usually related to the temperature of an object that is emitting radiation.
Absorption & emission line spectra are related to the composition of the material absorbing or emitting radiation.

43. Kirchhoff’s Laws
1. A hot, dense glowing object (solid or gas) emits a continuous spectrum.

44. Kirchhoff’s Laws
2. A hot, low density gas emits light of only certain wavelengths – an emission line spectrum.

45. Kirchhoff’s Laws
3. When light having a continuous spectrum passes through a cool gas, dark lines appear in the continuous spectrum – an absorption line spectrum.

47. Rules for Thermal Emission by Opaque Objects
Hotter objects emit more total radiation per unit surface area.
Hotter objects have their peak radiation at shorter wavelengths (they will appear “bluer”)

48. The sun emits its peak radiation in the yellow portion of the visible spectrum At “room temperature”, or “body-temperature”, an object emits its peak radiation in the infrared.

49. Now, let’s apply these rules.
Reiterating…
Hotter objects emit more total radiation per unit surface area.
Hotter objects have their peak radiation at shorter wavelengths (they will appear “bluer”)
Now, let’s apply these rules.

50. Which of the two stars (A or B) emits light that has a peak emission with the longer wavelength?
(red) Star A
(blue) Star B
(green) The stars’ peak emissions are at the same wavelength
(yellow) None of the above
visible range A
Energy output per second B
VIBGYOR
Wavelength

51. Which of the two stars (A or B) emits light that has a peak emission with the longer wavelength?
(red) Star A
(blue) Star B
(green) The stars’ peak emissions are at the same wavelength
(yellow) None of the above
visible range A
Energy output per second B
VIBGYOR
Wavelength

52. Which of the two stars (A or B) would appear red?
(red) Star A
(blue) Star B
(green) Neither would appear red
(yellow) There is insufficient information to determine the star’s color
visible range A
Energy output per second B
VIBGYOR
Wavelength

53. Which of the two stars (A or B) would appear red?
(red) Star A
(blue) Star B
(green) Neither would appear red
(yellow) There is insufficient information to determine the star’s color
visible range A
Energy output per second B
VIBGYOR
Wavelength

54. The figure shows the spectra of two stars. Which star is hotter
The figure shows the spectra of two stars. Which star is hotter? (red) A (blue) C (yellow) neither
visible range A
Energy output per second C
VIBGYOR
Wavelength

55. The figure shows the spectra of two stars. Which star is hotter
The figure shows the spectra of two stars. Which star is hotter? (red) A (blue) C (yellow) neither
visible range A
Energy output per second C
VIBGYOR
Wavelength

56. Which of the following is possible to infer about stars A and C based upon the information provided in the graph?
(red) Star A is smaller than star C
(blue) Star A is larger than star C
(green) The stars are the same size
(yellow) It is not possible to infer any of these relationships
visible range A
Energy output per second C
VIBGYOR
Wavelength

57. Which of the following is possible to infer about stars A and C based upon the information provided in the graph?
(red) Star A is smaller than star C
(blue) Star A is larger than star C
(green) The stars are the same size
(yellow) It is not possible to infer any of these relationships
visible range A
Energy output per second C
VIBGYOR
Wavelength

58. Electron Energy Levels
Electrons cannot have just any energy while orbiting the nucleus.
Only certain energy values are allowed (like the floors of an aprtment building).
Electrons may only gain or lose certain specific amounts of energy (equal to differences in energy levels).

59. This diagram depicts the energy levels of Hydrogen.
Each element (atom and ion) has its own distinctive set or pattern of energy levels.
This diagram depicts the energy levels of Hydrogen.
1 eV = 1.60 x joules

60. How can electrons absorb or emit energy?
By absorbing or emitting light
Through collisions of parent atom with another atom

61. Emission/Absorption Spectra
Each electron is only allowed to have certain energies in an atom.
Electrons can absorb light and gain energy or emit light when they lose energy.
Hydrogen
Only photons whose energies (colors) match the “jump” in electron energy levels can be emitted or absorbed.

63. Absorption Spectra
If light shines through a gas, each element will absorb those photons whose energy match their electron energy levels.
The resulting absorption line spectrum has all colors minus those that were absorbed.
We can determine which elements are present in an object by identifying emission & absorption lines.

64. Group Activity
A look at different types of spectra, as predicted by Kirchhoff’s Laws
Be sure to put your group name on the paper!!!

65. A. The white dwarf star (a thermal radiator) in the center of the nebula.
B. A distant star (that is much hotter than the gas) viewed through the cold gas expelled by the dying star.
C. An empty, dark region of space.
D. The diffuse gas expelled by the dying star seen against the dark background of space.
E. What type of element(s) do you expect to see in some of these spectra? Why?
What kind of spectrum is seen at each location depicted below? Explain.

66. Molecules have rotational & vibrational energy levels
(less energetic than electron energy levels, energies correspond with infrared, microwave, and radio radiations)

68. The Doppler Shift: A shift in wavelength due to a wave emitter moving towards (shorter wavelength) or away (longer wavelength) from an observer.

69. The Doppler Effect
 v
 c =

70. The Doppler Effect BLUESHIFT REDSHIFT
1. Light emitted from an object moving towards
you will have its wavelength shortened.
BLUESHIFT
2. Light emitted from an object moving away from
you will have its wavelength lengthened.
REDSHIFT
3. Light emitted from an object moving
perpendicular to your line-of-sight will not
change its wavelength.

71. Measuring Radial Velocity
We can measure the Doppler shift of emission or absorption lines in the spectrum of an astronomical object.
We can then calculate the velocity of the object in the direction either towards or away from Earth. (radial velocity)
 v
 c =

72. Measuring Rotational Velocity

73. If the wavelength of an electromagnetic wave increases, its velocity
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information

74. If the wavelength of an electromagnetic wave increases, its velocity
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information

75. If the wavelength of an electromagnetic wave increases, its frequency
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information

76. If the wavelength of an electromagnetic wave increases, its frequency
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information

77. If the wavelength of an electromagnetic wave increases, its energy
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information

78. If the wavelength of an electromagnetic wave increases, its energy
(red) Decreases
(yellow) Increases
(blue) Remains the same
(green) Not enough information