(b) two main types of atom packing with high efficiency are hexagonal close packing (hcp) and cubic close packed (ccp). [20 marks] (61) draw the atom packing models for the two types and show the atomic concentrations (atoms per unit volume) in each case. mark the atom positions on the models. [10 marks] (62) using trigonometric relationships in each of the two models of atom packing in (b1), calculate the volume for the two packed structures. [10 marks]. full marks will awarded for showing the stepwise calculation, as in the examples shown in the class exercise. (c) density computation exercise (15 marks] hematite and magnetite are two main fe-oxides, and are composed of fe and o. hematite has hexagonal close packing (hcp) and magnetite has "cubic diamond type" packing, i. e., combining cubic close packed (ccp) and face centred cubic (fcc). (see example used in class). hematite crystallises in the hexagonal system with cell parameters: a = b = 5.038 a, c=13.772a, and angles a = b = 90°; and y = 1200. magnetite is cubic with a = b = = 8.397 a, a = b = y = 90° given the atomic masses of fe and o as 55.845 g/mol, and 15.999 g/mol, respectively, calculate the density of hematite and magnetite. hints: use the following relationships for your density calculations. if mat is the atomic mass in the periodic table (given above for each element) then the mass of the atom (mat) in kg is: (1) mat= (103 kg/g)mat/na where nais avogadro's number na=6.023x1023 atom/mol and density is: (2) p = (number of atoms per unit volume) (mass per atom).