The crystal structure of iron (fe) is bcc at temperatures below 912°c and fcc above 912°c. complete parts () below. (a) sketch one unit cell of iron at the temperatures above and below 912°c. (show every atom in the unit cell as a dot or a small circle.) (b) using the known formulas for the atomic packing factor, calculate its values for iron above and below 912°c. (c) using the known formulas for the theoretical density, calculate its values for iron above and below 912°c.