1. 2-4 Elements and Compounds

2. Elements  An element is a substance that can not be broken down into simpler substances.  There are more than 100 known ones today  Yes you will memorize many of them.

4. Compounds  When two or more elements combine in a chemical reaction, they form compounds  They are a substance that forms in fixed proportions. –Example Magnesium Oxide, MgO, is always formed in this proportion.

5.  How can you tell them apart?  Both are pure substances  Possible to use a technique called electrolysis in which electricity separates into the elements. –Example: Electrolysis of water produces oxygen and hydrogen gasses.