Chapter 9: Chemical Formulas & Compounds Science 10 Unit 2 Chapter 9: Chemical Formulas & Compounds SC10 2-1

Types of Bonds There are three main types of bonds: Ionic Bonds: between metals and non-metals 2. Covalent Bonds: between non-metal atoms 3. Metallic Bonds: between metal atoms SC10 2-2

Ionic Compounds The nonmetal atom “steals” an e- from the metal atom - + The non-metal becomes a (-) ion and the metal becomes a (+) ion Since they are oppositely charged ions, they attract each other and stick together They will form a “crystal lattice” structure rather than separate molecules SC10 2-3

Ions Note: to tell at a glance what kind of ion an element will form, look at the periodic table. Group I: (Alkali Metals) +1 II: (Alkaline Earth Metals) +2 III: (Aluminum, etc.) +3 IV: (Carbon, etc.) ± 4 V: (Nitrogen, etc.) -3 VI: (Oxygen, etc.) -2 VII: (Halogens) -1 SC10 2-4

1. Writing Formulas Mg O Mg O MgO e.g. Magnesium oxide 1. Write both symbols (+ion first) with ion charge 2+ 2- Mg O 2. Criss-cross the charges and write them as subscripts Mg O 2 2 MgO 3. Reduce if possible (remember, the subscript 1 is never written) SC10 2-5

More Examples! Al S Al S Al2S3 Ca Cl Ca Cl CaCl2 Aluminum sulphide 3+ 2- Aluminum sulphide Al S Al S Al2S3 2 3 2+ 1- Ca Cl Calcium chloride Ca Cl CaCl2 1 2 SC10 2-6

Sometimes, metal ions have more than one combining capacity e.g. Cu2+ Cu1+ Fe3+ Fe2+ The name of the compound will include a roman numeral that tells you which combining capacity to use e.g. Iron II oxide Iron III oxide 2+ 2- 3+ 2- Fe O Fe O Fe O Fe O 2 2 2 3 FeO Fe2O3 (cannot be reduced) SC10 2-7

Assignment In Class: Formula Assignment #1 & #2 (formulas only, no naming) Homework: Read pages 193 to 198 Page 198 “Review 9.2” Q: 1-8 Finish Formula Assignment #2 SC10 2-8