In the Goldschmidt correction, relative factors used to adjust this quantity are based on 12-fold coordinated close-packed structures. A different quantity named for Allred and Rochow equals 3590 times Z-effective over this quantity squared. The Hume-Rothery rules state a substitutional alloy will only form if this quantity for two elements is within 15% (15[1])of each other. A “hard sphere” model can be used to calculate the (*) van der Waals form of this quantity. (10[1])Poor shielding against nuclear charge by 4f electrons explains why this (10[1])quantity “contracts” for (10[2])lanthanides. Like metallic character, this quantity decreases from left to right across a (10[1])period and increases down a group. For 10 points, an atom’s size is measured by what distance between an atom’s nucleus and outermost electron? ■END■