Lesson C4.1 http://www.rsc.org/Education/Teachers/Resources/ptdata/welcome.htm
www.webelements.com
http://www.rsc.org/periodic-table/
www.periodicvideos.com
Lesson C4.4
www.wfu.edu/~ylwong/balanceeq/balanceq.html
http://members.misty.com/don/spectra.html
Lesson C4.12
http://www.mindsetsonline.co.uk/index.php?cPath=18_186_502
www.daviddarling.info/encyclopedia/K/Kirchhoff.html
http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/ramsay.html
www.webelements.com/helium/history.html
