Enter lower-case "y" from keyboard to brighten display. Toggle "t" key and select most pleasing line width. Toggle Na and Cl buttons to identify atoms. This display uses Na to define the FCC, but Cl could have been used equally well. Click-on adjacent corners of the cell to measure the distance between them (as displayed in lower-left corner of graphics window). To what cell parameter is this distance related? (answer: cell constant a = 5.62 Å) Verify the density of sodium chloride by calculation. What is the distance between nearest sodium and chlorine atoms? (answer: Na - Cl distance = 2.81 Å) Toggle Space Fill button. Note only the larger green spheres make contact with each other. If they were used to define the FCC, then 4 green radii would be in contact on a Face-Diagonal. Consider the geometry of the cell and display distances between its various parts. What is the radius of a green sphere? a blue sphere? (answers: radius green = 1.99 Å - face-diagonal = 7.95 Å and four Cl radii lie on it; blue = 0.82 Å - cell edge = 5.62 Å and 2 Cl and 2 Na radii lie on it) Clear Space Fill button and check C.N. of Cl button to display six "bonds" to six Na atoms - all at vertices of an octahedron. Check C.N. of Na button to display six "bonds" to six Cl atoms - also at vertices of an octahedron. Na and Cl have equivalent surroundings. Check All button to show all "bonds" within this cell and beyond. Clear All button. FCC unit cells display a 5 - 4 - 5 pattern when sliced paralled to a cell Face. When sliced perpendicular to the Body-Diagonal, a 3 - 7 - 3 pattern is displayed showing ABC closest-packed layering. Check ABC Packing button and those under it to display the 3 - 7 - 3 pattern. Open View window and select VIEW 2 to view directly down a body-diagonal, and sequence these buttons again. Try to observe this view in "cross-eyed" stereo. (Reduce ZOOM to about 0.5 and enter lower case "s" key and then lower case "c" key.) Move model by placing cursor in graphics window and then click-and-drag mouse.