Today we introduced the concept of “phase changes.” I began the lesson with a brief description of why certain molecules are magnetic. Water is, of course, the classic example. Because the electrons in the hydrogen atoms are bonded with the oxygen atom below, the top of a water molecule takes on a small positive charge, while the bottom takes on a small negative charge. This lesson is not necessarily part of the 8th grade curriculum, but it is important background for understanding phase changes.
After that, we went through a PowerPoint on phase changes (posted below). It explained all five phases of matter, why molecules tend to clump together, and the names of the four common phase changes (melting, freezing, boiling, and condensing). At the end of class, I decided to spice things up a bit with a dry ice demonstration.