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 (-5[1])equals 3590 times Z-effective over this quantity squared. (-5[1])The Hume-Rothery rules state a substitutional alloy will only form if this quantity for two elements is within 15% of each other. A (15[1])“hard sphere” model can be used to calculate the (*) van der Waals form of this quantity. Poor shielding against nuclear charge by 4f electrons explains why this quantity “contracts” for (10[1])lanthanides. Like metallic character, this quantity decreases from left to right across a period and increases down a group. For 10 points, an atom’s size is measured by what distance between an atom’s (10[1])nucleus and outermost electron? ■END■