One mole of nickel (6 1023 atoms) has a mass of 59 grams, and its density is 8.9 grams per cubic centimeter, so the center-to-center distance between atoms is 2.23 10-10 m. You have a long thin bar of nickel, 2.7 m long, with a square cross section, 0.08 cm on a side. You hang the rod vertically and attach a 67 kg mass to the bottom, and you observe that the bar becomes 1.39 cm longer. From these measurements, it is possible to determine the stiffness of one interatomic bond in nickel.