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.

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

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)

Is there a problem with perpetual motion machines?

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

Atom nucleus electron p+ e- n proton neutron

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

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.

Incorrect view better view

The particles in the nucleus determine the element & isotope.

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

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

Atomic Number. Element. 1. Hydrogen (H). 2. Helium (He). 3 Atomic Number Element 1 Hydrogen (H) 2 Helium (He) 3 Lithium (Li) 4 Beryllium (Be) 5 Boron (B) 6 Carbon (C) 7 Nitrogen (N) 8 Oxygen (O) Each of these have multiple isotopes, some of which are not stable

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

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.

Three isotopes of Carbon, two stable, one unstable. Three isotopes of Hydrogen, two stable, one unstable. 1H 2H 3H 12.32yr 99.9816% 0.0184%

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

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

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)

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

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

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

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

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

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

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

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

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:

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

Why does evaporation cool a liquid (consider perspiration)?

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

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)

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 

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!

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.

The Electromagnetic Spectrum lower energy higher energy

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

Got here

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.

Different wavelengths of light interact differently with the atmosphere

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

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.

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

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

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.

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”)

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.

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.

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

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

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

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

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

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

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

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

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).

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 10-19 joules

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

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.

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.

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!!!

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.

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

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

The Doppler Effect  v  c =

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.

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 =

Measuring Rotational Velocity

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

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

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

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

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

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