Review session: Tonight, 7:00-8:00 pm, Swain East 010 Homework #3 is due by 5:00 pm Exam #1 on Wednesday It will cover the material covered in the nine class sessions to date (including today) Review session: Tonight, 7:00-8:00 pm, Swain East 010

Every element has multiple isotopes same number of protons (same element) different numbers of neutrons

Unstable isotopes and radioactivity Unstable (“radioactive”) isotopes “decay”, producing a new type of atom, i.e., an atom of a different element OR a different isotope of the original element. One half of the atoms of an unstable isotope decay in one “half-life” of that isotope.

Three isotopes of Carbon, two stable, one unstable. 5730 yrs 14C  14N + electron + antineutrino + energy Mass (14C) > Mass (14N + electron + antineutrino)  difference in mass is converted into energy: E = mc2

Tritium is an unstable isotope of Hydrogen (1p,2n) with a half life of 12.3 yrs. If a sample of hydrogen initially has 1000 atoms of Tritium, how many will remain after 36.9 yrs (two half-lives)? (yellow) 1000 (red) 500 (green) 250

Tritium is an unstable isotope of Hydrogen (1p,2n) with a half life of 12.3 yrs. If a sample of hydrogen initially has 1000 atoms of Tritium, how many will remain after 36.9 yrs (two half-lives)? (yellow) 1000 (red) 500 (green) 250

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

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

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 (yellow) a fission reaction (red) a different element with a positive charge (green) a neutron and a positron

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 (yellow) a fission reaction (red) a different element with a positive charge (green) a neutron and a positron

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

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

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 (yellow) a molecule (red) a different element (green) an ionized atom

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 (yellow) a molecule (red) a different element (green) an ionized atom

Absorption & Emission Line spectra

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).

Electron Orbits / Absorption & Emission Electrons can gain or lose energy while they orbit the nucleus. When electrons have the lowest energy possible, we say the atom is in the ground state. When electrons have more energy than this, we say the atom is in an excited state. When electrons gain enough energy to escape the nucleus, we say the atom is ionized.

This diagram depicts the energy levels of Hydrogen. Each element has its own distinctive set of energy levels for its electrons. This diagram depicts the energy levels of Hydrogen. 1 eV = 1.60 x 10-19 joules

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.

C B D E 1 eV = 1.60 x 10-19 joules A F

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

A B

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

A B

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.

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

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.

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