1. Kepler 1: planet with two suns

2. Homework #3 Due Wednesday, 11:00 p.m. Answers to all homework questions will be posted on the class website First exam: Monday, October 3.

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

4. Three isotopes of Carbon, two stable, one unstable. 5730 yrs 14 C  14 N + electron + antineutrino + energy Mass ( 14 C) > Mass ( 14 N + electron + antineutrino)  difference in mass is converted into energy: E = mc 2

5. Unstable (radioactive) isotopes decay into daughter atoms, with decay rates specified by the isotope’s “half-life” EXAMPLE: RADIOCARBON DATING The half-life of 14 C is 5730 years Assume a living organism contains 10 6 atoms of 14 C while it is alive. Elapsed time (years) Number of half lives 14 C atoms 14 N atoms( 14 N / 14 C) 001,000,00000 5,7301500,000 1 11,4602250,000750,0003 22,9203125,000875,0007 45,840462,500937,50015

6. p+p+ n e-e- n p+p+ Another term to know: Ion Atom with one or more electron(s) missing - cation Atom with one or more extra electron(s) - anion ion He +1 How to create a cation: * Collisions between atoms in a high temperature gas * Absorption of photon with sufficient energy to strip off an electron

7. Two or more atoms combined to form a new particle - molecule p+p+ p+p+ 8p + 8n molecule H 2 O (water) Sharing of electrons (chemistry) is involved in the construction of molecules Dissociation: Breaking apart a molecule (e.g., energetic collisions, absorption of energetic photon

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. Absorption & Emission Line spectra

17. 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).

18. 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.

19. 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

20. 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. Only photons whose energies (colors) match the “jump” in electron energy levels can be emitted or absorbed. Hydrogen

21. 1 eV = 1.60 x 10 -19 joules A B C DE F Not allowed? Ionized? Shortest wavelength photon produced? Longest wavelength photon absorbed?

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

25. 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.

26. 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.

28. Molecules have rotational & vibrational energy levels – often showing spectral lines in the infrared and radio portion of the electromagnetic spectrum

30. 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!!!

31. 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.