Glaxo Smith Kline's Active Science offers fifteen interactive games covering a range of science topics.
The Interactive Periodic Table is a game designed to help chemistry students practice identification of the elements. To play the game students are given some clues about an element's properties. Using those clues the student has to place the element in the correct place on the table.
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The Ptable is another interesting tools: put the mouse over the element and visualize all the information about it.