Derek A. Davenport, Robert B. Fosterling, and Viswanathan Srinivasan Purdue University West Lafayewe, Indiana 47907
Molar Volumes: Microscopic Insight from Macroscopic Data
All beginning students know that the molar volume of any eas at STP is close to 22,400 cm3 and in a eeneral way most L o w the implications ofthat remarkable &umstanie. Few such students calculate the values of 18.02 cm3 for the molar volume of liquid water, 19.65 cm3 for ice, and 26.99 cm3 for sodium chloride under the same conditions. Fewer still would ponder these values beyond the obvious implication that the microscopic particles are about ten times further apart in the standard s~~~~ easeous state than in twical .. condensed ~ h a s e sI. t is true that Lothar Meyer's molar (atomic) volume versus atomic weieht lot is often cited for its ~ronouncedDeriodicitv but in generaithe matter is then quiktly dropped. And yet molar volumes can clearly tell us a great deal about relative (and even, with a knowledge of N, absolute) size, a subject quite properly considered to be of major importance in today's courses. c atomic, molecular, and ionic size is commonly The t o ~ i of taught h i fiat since interpretation of X-ray diffraction patterns is considered by all l)ur the most visionary u)he beyond the capabilities of
