links. taula per.www.learner.org.docx
http://www.learner.org/interactives/periodic/basics_interactive.html
http://www.learner.org/interactives/periodic/elementary_interactive.html
http://www.learner.org/interactives/periodic/box_interactive.html
http://www.learner.org/interactives/periodic/groups2.html
http://www.learner.org/interactives/periodic/groups_interactive.html