1. 3.2 Naming Chemical Compounds and Writing Formulae
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2. Rules for Naming Ionic Compounds: Positive ion (metal) is always first
Negative ion (non-metal) is always second
Non-metal ion’s name ends with the suffix “-ide”
Practice:
BaCl2
NaF
Al2O3
See page 85

3. Practice (cont.):
4. K2S
5. CaO
6. Ba3P2
7. Na2O
8. BeS

4. (c) McGraw Hill Ryerson 2007
Formulas of Ionic Compounds
In an ionic compound, the positive charges balance the negative charges.
You need to determine the smallest whole number ratio of positive to negative ions.
See page 87
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5. Rules for writing ionic formulae:
Identify each ion and its charge. (Metal first then non-metal)
Determine the smallest number of charges needed to balance out the +’s and –’s
Write this ratio in subscript form (Note: do not write ones)
Ex. 1: zinc nitride
Ex. 2: aluminum chloride

6. Short-cut: “Swap and Drop”
Write each element’s symbol with their charges
The charge (without the sign) of one ion becomes the subscript of the other ion.
Reduce subscripts to the smallest whole numbers that keep the ration of ions.

7. Why this works:
Consider beryllium fluoride:

8. Practice!
Na and Cl
Ba and F
K and S
Al and I
Ag and O

9. Multivalent Metal Compounds
Many metals are multivalent, meaning the metals form two or more different positive ions with different charges
For ex., the atom iron forms two ions Fe2+ and Fe3+
Use roman numerals to distinguish between the ions.
For ex., Fe3+ would be named “iron(III)”
See page 88
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10. Know your Roman numerals!
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11. Writing Multivalent Formulas
Same rules as regular ionic compounds but you don’t have to look up the charges (a.k.a. combining capacity) on the metal – just look at the roman numeral!
Practice:
Copper (I) chloride
Copper (II) chloride
Cobalt (III) oxide
Manganese (IV) sulphide
See page 89
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12. Multivalent Compound Names
Steps to writing multivalent compound names are as follows:
Identify the metal and verify it forms more than one ion.
Look at the formula and reverse “swap & drop”.
Check the periodic table to see what the charge on the non-metal & to make sure the ratio hasn’t been reduced.
For example: Fe2O3
See page 90
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13. Writing the Formula of Polyatomic Ion (PAI) Compounds
Write the ions and their charges.
“Swap and drop”.
Reduce if necessary
For example:
Ammonium sulphide
Magnesium nitrate
See page 91
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14. Writing the Names of Polyatomic Ion (PAI) Compounds
Verify a polyatomic atom is present.
Name the positive ion and decide if a roman numeral is necessary.
Name the negative ion and if it is a polyatomic ion, do NOT change the ending on the name.
For example:
Na3PO4
(NH4)2CO3
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15. Practice:
Write the formula for:
sodium nitrate
potassium acetate
aluminum sulfate
lithium chlorate
magnesium nitrate

16. 2. Write the name:
KNO3
Ba(OH)2
Li2CO3
Fe2(SO4)3
NH4ClO3