Greetings all, My first problem: I have been asked to derive the minimum radius ratio for coordination numbers 4 and 6. I read the book and looked at the sample problems, but they do not help at all. I realize that it has to do with the geometry of it, but have no idea how to use that. The book is: INTRODUTION TO MATERIALS SCIENCE FOR ENGINEERS (6th edition) by James F. Schackelford. My second problem: How does one calculate the rxn energy for polymerization of styrene (C_3H_6). We are given various bond energies for single carbon - carbon bonds at different lengths. I drew it and looks like: c - c = c w/ H atoms around it. In an example, the picture is: c = c and they broke it down into 2(c - c). how would i do it for 3 carbons? Also, how would I know what the bond length is (since the bond energies are related to them)?