Chemical substance identity of benzene, until the correct structure was described by Friedrich August Kekulé. Likewise, the idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it
Magic Tree House Magic Tree House Merlin Mission Books 1-27 were written for more advanced readers. They are more challenging adventures for readers ages 7–10. The Magic Tree House Merlin Missions were originally ordered sequentially, starting at Book #29 (Christmas in Camelot). With the 25th anniversary re-prints, the books have been separated into their own distinct series and re-numbered starting at Merlin Mission #1. On January 6, 2015, the first Magic Tree House Super Edition was released. It is 183 pages long. The super editions are longer than the original Magic Tree House books and the Magic Tree House Merlin Missions. The Magic