Useful Links
Useful Links:
http://www.lenntech.com/periodic/periodic-chart.htm
http://cd1.edb.hkedcity.net/cd/science/chemistry/resource/vc/VC_Part2/html_en/introduction.html
http://boomeria.org/chemtextbook/chemtextmenu.html
https://www.thoughtco.com/chemistry-4133594
http://www.chemicalelements.com/