Molecule Polarity

This was just an introduction to polarity. We will be exploring this more in the next lesson.

Our task was to determine the polarity of the molecules we did ball-and-stick diagrams for in yesterday's lesson.

Here are a couple of observations we need to be able to explain, using molecular polarity:

1. Polar solutes dissolve better in polar solvents. Non-polar solutes are only sparingly soluble in polar solvents. Why? The example we were given was ammonia (NH₃) dissolving in water.

   

   SOURCE: UC Davis ChemWiki



SOURCE: http://www.ausetute.com.au/lewisstr.html

2. Polar molecules have higher melting and boiling points than non-polar molecules with a similar-sized electron cloud. For example, methane (M_R = 16.0 gmol^-1) is a gas at room temperature while water (M_R = 18.0 gmol^-1) is a liquid. Why?

   

   SOURCE: http://chemsite.lsrhs.net/bonding/lewis_dots.html

   
   

SOURCE: http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s15-02-intermolecular-forces.html