In the basic CsCl (cesium chloride) crystal structure, Cs+ ions form the corners of a cube and a Cl- ion is at the cube's center (see right figure). The edge length of the cube is 0.40 nm. The Cs+ ions are each deficient by one electron (and thus each has a charge of +e), and the Cl - ion has one excess electron (and thus has a charge of -e). (a) What is the magnitude of the net electrostatic force exerted on the Cl - ion by the eight Cs+ ions at the corners of the cube? (b) If one of the Cs+ ions is missing, the crystal is said to have a defect; what is the magnitude of the net electrostatic force exerted on the Cl - ion by the seven remaining Cs+ ions?