1. Chapter 17 Chemical Bonds and Compounds October 7, 2009

2. Key Concept Elements combine to form compounds.

3. I. Compounds have different properties from the elements that make them. A. Compound- pure substance made of atoms of 2+ different elements (alphabet of elements) B. Chemical Bond- how atoms of different elements are held together in compounds

4. B. Properties also depend on how atoms are arranged in the compound. C. Properties in compounds can be COMPLETELY different than those of it’s element parts H 2 O Calcium + Chloride Quick Check: How do the properties of a compound compare with the properties of the elements that make it?

5. Chemical Formulas A. Chemical Formulas use chemical symbols to represent the atoms of the elements and their ratios in a chemical compound

6. B. How do I write a chemical formula? *Let’s take Carbon Dioxide* 1. Find the symbols for Carbon and Oxygen on the periodic table. Write these symbols down side by side. 2. To indicate that there are two oxygen atoms for every carbon atom, place the subscript 2 to the right of the oxygen atom’s symbol. *a subscript is a number written to the right of a chemical symbol and slightly below it*

7. 3. Because there is only one atom of carbon in carbon dioxide,,you need no subscript for carbon. The subscript 1 is never used. The chemical formula for carbon dioxide is…

8. Key Concepts! Please answer these questions in your notebook. 1. How do the properties of compounds often compare with the properties of the elements that make them? 2. How many atoms are in the compound represented by the formula C 12 H 22 O 11 ? 3. If a chemical formula has no subscripts, what can you conclude about the ratio of the atoms in it?

9. Homework Practice! Due Tomorrow! Directions: Identify how many atoms of each element there are in the following compounds 1. Silver Fluoride AgF 2. Aluminum Chloride AlCl 2 3. Borazine B 3 H 3 N 6 4. Propane C 3 H 8 5. Citric Acid C 6 H 8 O 7