A Closer Look at Trends in Boiling Points of Hydrides:: Using an Inquiry-Based Approach To Teach Intermolecular Forces of Attraction

• Samantha Glazier ^[1] ; Nadia Marano ^[1] ; Laura Eeisen ^[2]
  1. [1] St. Lawrence University

     St. Lawrence University

     Town of Canton, Estados Unidos

     
  2. [2] George Washington University

     George Washington University

     Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 87, Nº 12 (December), 2010, págs. 1336-1341
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • We describe how we use boiling-point trends of group IV−VII hydrides to introduce intermolecular forces in our first-year general chemistry classes. Starting with the idea that molecules in the liquid state are held together by some kind of force that must be overcome for boiling to take place, students use data analysis and critical reasoning to discover different types of intermolecular forces. In general, dispersion forces provide the largest contribution to the strength of the total intermolecular interaction energy, whereas dipole forces add only a small contribution, except in the case of molecules that can form hydrogen bonds. We discuss the thermodynamics of boiling and why it is legitimate to use boiling point as a measure of intermolecular forces. Finally, we examine the choice of variable to use on the x axis when graphing boiling point. Although the molecular polarizability may be a good variable to use, because it is the largest component of the interaction energy, the number of electrons is sufficiently well correlated with polarizability to recommend using boiling point versus number of electrons as the best compromise for introductory chemistry classes.