1. Elements are pure substances that can not be broken down into simpler substances. Ex. Calcium, Hydrogen, Fluorine A pure substance is one that contains only one type of particle. Ex. Sugar contains only sugar particles Compounds are pure substances that contain two or more different elements in a fixed proportion or ratio. Ex. H 2 O contains only hydrogen and oxygen atoms - 2 hydrogen atoms for every one oxygen atom

2. A molecule contains two or more atoms joined together. The atoms may all be the same - Ex. O 2 is an oxygen molecule with two oxygen atoms joined together. The atoms may be different - Ex. CH 4 (methane) or CH 3 COOH (vinegar) Proportion is important! Sugar, C 12 H 22 O 11 also contains C, H and O (like vinegar) but the proportion is different

3. Chemical Formulas The chemical formula is a combination of chemical symbols that represents a compound. It tells us what elements are present and in what proportion or ratio. The subscripts in the formula tell us how many atoms of a particular element are present in the compound.

4. Examples Sugar - C 12 H 22 O 11 Vinegar - CH 3 COOH - 12 carbon atoms - 2 carbon atoms - 22 hydrogen atoms - 4 hydrogen atoms - 11 oxygen atoms - 2 oxygen atoms Ratio = 12C:22H:11O Ratio = 2C:4H:2O Same elements but in a different proportion!

5. Now You Try! Sodium bicarbonate (baking soda!) – NaHCO 3

6. Now You Try More! Calcium phosphate (fertilizer) – Ca 3 (PO 4 ) 2

7. …and more! Text book : page 47 # 3 and 4 page 59 # 3, 4 and 5 Worksheet