Free science materials
As soon as you get to study the sciences in their own right, usually at the start of secondary school, everything suddenly seems to get harder. When you study Chemistry, understanding the periodic table is one of the most essential requirements. Grasp that and a lot of Chemistry and other science- related subjects suddenly make more sense. It can be a help for other subjects like Geography where some science knowledge helps us understand issues in the environment and therefore how to solve them.
So we love this free interactive periodic table which is great for students and teachers.