1. Chapter 9: Chemical Formulas & Compounds
Science 10 Unit 2
Chapter 9:
Chemical Formulas
& Compounds
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2. 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
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3. 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
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4. 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
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5. 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)
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6. More Examples! Al S Al S Al2S3 Ca Cl Ca Cl CaCl2 Aluminum sulphide3+ 2-
Aluminum sulphide Al S
Al S
Al2S3 2 3 2+ 1- Ca Cl
Calcium chloride
Ca Cl
CaCl2 1 2
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7. 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)
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8. 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
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