1. Briefly cite the main differences between ionic, covalent, and metallic bonding. 2. What is the difference between an allotrope and a polymorph? 3. What is the difference between atomic structure and crystal structure? 4. Bromium has two naturally occurring isotopes: 79Br, with an atomic weight of 78.918 amu, and 81Br, with an atomic weight of 80.916 amu. If the average atomic weight for Br is 79.903 amu, calculate the fraction-of-occurrences of these two isotopes. 5. What is the electronegativity of C considering SiC is 11% ionic and Xsi = 1.8? 6. A hypothetical metal has the BCC crystal structure, a density of 7.24 g/cm', and an atomic weight of 48.9 g/mol. Calculate the atomic radius of this metal. 7. Zirconium has an HCP crystal structure and a density of 6.51 g/cm3. (a) What is the volume of its unit cell in cubic meters? (b) If the c/a ratio is 1.593, compute the values of c and a. Consider the unit cell volume, Vc = 6R2cv3