4/21: why things float
http://www.screencast.com/t/MWZjZGY4YT

4/21: why things sink
http://www.screencast.com/t/ODA4ODJkM2Ut

3/23: ionic compound names and formulas
http://www.screencast.com/t/ZDExYTZhNTEt

3/23: K2O ionic compound formation
http://www.screencast.com/t/N2FlNWMz

3/17: CoCl3 formation
http://www.screencast.com/t/OWZmOTQzODYt
 
3/17: forming ionic compounds
http://www.screencast.com/t/M2RhODY0M

3/16: ions and oxidation numbers
http://www.screencast.com/t/OTc3MGM3N2

3/16: Lewis-dot structure
http://www.screencast.com/t/YTFkYjQxMD