1. Ch 9: Origin of Element Abundances in the Universe: Primordial Composition: 77% Hydrogen, 23% Helium, 3 parts per billion Lithium Current Composition: 74% Hydrogen, 24% Helium, 2% elements number 3-92 (everything else) Where did the extra 1% Helium and 2% everything else come from?

2. Nuclear reactions in stars are responsible for the current element abundance of our universe. They are also responsible for the generation of energy by stars (sunlight). You need to understand something about nuclear reactions to understand the presence of chemical elements and energy in the universe!

3. Four Forces of Nature: ForceActs OnRange 1)Gravityall masslong 2)Electromagneticp, elong 3)Strong Nuclearp, nshort 4)Weak Nuclearp, nshort p = proton, n = neutron, e = electron long range = infinite short range = 10 -15 m (size of a nucleus)

4. Four Forces of Nature (Cont): ForceEffect 1)Gravityalways attractive 2)Electromagneticopposite charges attract/like charges repel 3)Strong Nuclearstrongly attractive over short range 4)Weak Nuclearchanges protons to neutrons & vice versa

5. Two Kinds of interactions involving Nuclei: 1.Fusion: Two small nuclei are drawn together by the strong force and release energy Fusion will release energy for nuclei lighter than Iron (element 26). 2.Fission: A large nucleus falls apart due to electric repulsion and releases energy Fission will release energy for nuclei heavier than Iron (example: uranium).

6. Nuclear fusion of Hydrogen into Helium is what powers 90% of all stars (including the Sun). Conditions Needed: 1.Need plentiful hydrogen 2.Need high temperatures (>10 million Kelvin) These conditions occur naturally in the cores of stars. High temperature fusion = Thermonuclear fusion Controlled fusion is probably the only viable long-term solution to energy problems on Earth!

7. Where does the energy in fusion come from? It comes from the conversion of a small amount of mass directly into energy. A consequence of Theory of Special Relativity: Energy can be converted directly into mass and mass can be converted directly into energy. Formula for the amount of energy produced: E = mc 2 (equation 9.7) c = speed of light (big number) c 2 = a really big number (lots and lots of energy)