1. Compounds

2. Elements Combined -most elements are not found alone in nature -often two or more elements chemically combine to form compound a pure substance called a compound -in order for elements to combine, they must react with one another (undergo a chemical change) EXAMPLES: table salt - sodium & chlorine water - hydrogen & oxygen glucose - carbon, hydrogen & oxygen carbon dioxide - carbon & oxygen

3. Definite Quantities - elements combine in specific ratios (according to atomic mass) in order to form compounds -the ratio of the mass of one element to the mass of another element in a compound is always the same, no matter how large the sample is EXAMPLE: Water - ratio is always 1:8 (1/8), 1 gram of hydrogen to 8 grams of oxygen If a sample of water had 3 grams of hydrogen, how many grams of oxygen would it contain? If a sample of water had 48 grams of oxygen, how many grams of hydrogen would it contain? What if the sample had 2 grams of hydrogen & 12 grams of oxygen?

4. Unique Properties -each compound has a unique set of properties -distinguish it from other compounds -compounds have their own physical and chemical properties -because compounds are formed by chemical reactions, they have different properties than the elements that form them EXAMPLE: table salt – NaCl composed of - sodium (reacts violently with water) - chlorine (poisonous gas) Na + Cl NaCl

5. Break-it-Down -compounds can be broken down into elements through chemical changes -some compounds break down when heated, others break down when introduced to electric current -still others react with acid, water, oxygen, etc. EXAMPLE: Heating mercury (II) oxide causes it to break down into mercury and oxygen. -some compounds form simpler compounds as a result of chemical change EXAMPLE: Opening a bottle of soda causes a chemical change in which carbonic acid breaks down into carbon dioxide and water. Those two compounds can then be broken down into carbon, oxygen, and hydrogen. -compounds cannot be broken down by physical changes!!

6. Compounds are EVERYWHERE -some very important compounds that occur in nature are proteins -proteins are nitrogen-based compounds used to construct and repair cells -as proteins are digested, they are broken down into smaller compounds that can be used by the cell -carbon dioxide is another important compound Why is it so important? It is used by plants to produce other compounds, like sugar, and elements like oxygen Glucose Molecule Oxygen Gas Molecule

7. -compounds are used heavily in industry -fertilizers, medicines, food preservatives, and synthetic fabrics are some examples of products created using compounds EXAMPLE: Nitrogen and hydrogen (both elements) are combined to form the compound ammonia, which is used to make fertilizers -compounds in nature usually must be broken down into the raw materials needed in industry EXAMPLE: Aluminum does not exist alone in nature; it is acquired by breaking down the compound aluminum oxide Fertilizer Aluminum Oxide (Corundum)