I found this introduction to the elements, and a breakdown of the periodic table on Chem4Kids – lots more interesting stuff on their site.

As far as we know, there are only so many basic elements. Up to this point in time we have discovered/created over 100. While there may be more out there to discover, the basic elements remain the same. Iron (Fe) atoms found on Earth are identical to iron atoms found on meteorites. The iron atoms on Mars that make the soil red are the same too.