The corundum (Al2O3) has a rhombohedral Bravais lattice, but itclosely approximates a hexagonal lattice and is usually regarded ashexagonal. There are 30 ions per lattice site (and per unit cell).The Al2O3 formula requires that these 30 ions be divided as 12Al3+and 18 O2-. The Al2O3 structure closely approximates close-packedO2- sheets with two-thirds of the small interstices between sheetsfilled with Al3+. In other words, close-packed O2- ion containinglayers have repeated stacking and the Al3+ ions fill two-thirds ofthe octahedral interstices between adjacent layers. (22 points) Thedensity of Al2O3 is ï²Al2O3 = 3.8 gram/cm3, Atomic masses are : MAl= 26.98 gram/mol, MO = 16.00 gram/mol Ionic radii are : rAl3+ =0.05 nm, rO2- = 0.14 nm a) Draw 3 layers/sheets of O2- ions andAl3+ ions in between them. b) Draw the corundum unit cell and showthe O2- and Al3+ ions in the unit cell. c) How many Al2O3 moleculesare there in 1 cm3 ? How many atoms are there in 1 cm3 of Al2O3? d)How many Al2O3 molecules are there in 1 gram? How many atoms arethere in 1 gram of Al2O3? e)Calculate the atomic packing factor ofAl2O3
