Question
Sat April 19, 2014 By: Rudra Yadav

 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? 

Expert Reply
Mon April 21, 2014
a) Opposite cs+ ions will attract cl- ions with equal and opposite forces along the four body diagonals and hence the net electrostatic force exerted on the cl- ions by the eight cs+ ions at the corners of the cube will be zero.
b) When one cs+ is missing ,net force along three body diagonals ions on cl- will cancel off ,so The seven remaining ions will exert a force of only one Cs ion opposite to the missing ion. the effect of the other six paired ions will be again zero .Hence the net force is
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