In Example 3.2, the relationship between lattice parameter, a, and atomic radius, r, for an fcc metal is found to be a=(4/2)r, as given in Table 3.3. Derive the similar relationships in Table 3.3 for (a) a bcc metal and (b) an hcp metal. PRACTICE PROBLEM 3.3 Calculate the density of -Fe, which is a bcc metal. (Caution: A different relationship between lattice parameter, a, and atomic radius, r, applies to this different crystal structure. See Practice Problem 3.2 and Table 3.3.)