1. Unit B Matter and Chemical Change Molecular Compounds

2. What is a Molecular Compound? This occurs when non-metals combine to form a pure substance called a molecular compound. This occurs when non-metals combine to form a pure substance called a molecular compound. The elements share electrons in what is called a covalent bond. The strength of this bond depends on the number of pairs of electrons that are shared. The elements share electrons in what is called a covalent bond. The strength of this bond depends on the number of pairs of electrons that are shared.

3. Writing Formulas for Molecular Compounds Similar to writing ionic compounds EXCEPT no ions are present and the ion charge is not used in the formula. Similar to writing ionic compounds EXCEPT no ions are present and the ion charge is not used in the formula. The formula still shows what elements are present and how many atoms of each are in the compound. The formula still shows what elements are present and how many atoms of each are in the compound.

4. Naming Molecular Compounds Rules: 1. The first element in the compound uses the element name (just like the ionic compounds do). 2. The second element has a suffix – ide – (like the ionic compounds).

5. Naming Molecular Compounds Rules (continued): 3. When there is more than 1 atom in the formula, a prefix is used which tells how many atoms there are: 4. Exception to #3 above – when the first element has only 1 atom the prefix mono is not used.

6. Naming Molecular Compounds The way to write molecular compounds is like this The way to write molecular compounds is like this Prefix +First Element Prefix + Second element (with “ide” ending)

7. Examples CO 2 carbon dioxide CO 2 carbon dioxide N 2 O dinitrogen monoxide N 2 O dinitrogen monoxide N 2 O 3 dinitrogen trioxide N 2 O 3 dinitrogen trioxide NF 3 nitrogen trifluoride NF 3 nitrogen trifluoride CCl 4 carbon tetrachloride CCl 4 carbon tetrachloride PF 5 phosphorus pentafluoride PF 5 phosphorus pentafluoride

8. Comparing Ionic and Molecular Compounds Look at the table on pg. 153 Look at the table on pg. 153 Make a note of in your notes Make a note of in your notes What are the differences we see between the two? What are the differences we see between the two?