1. 4.2 Names and Formulas of Compounds

2. Chemical Names
All ionic compounds are composed of positive and negative ions
The chemical name indicates which elements are present in the compound
Each name has two parts:
One for the positive ion
One for the negative ion

3. Chemical Names To Name an Ionic Compound: Name the positive ion:
- it’s the same as on the periodic table
Name the negative ion
-drop the end of the element name and add “ide”

4. Examples: NaCl KBr CaF2 4. MgO Sodium chloride Potassium bromide
Calcium fluoride
Magnesium oxide

5. Chemical Formulas Symbols represent the elements in the compound
Subscript numbers following the symbol show how many of each element are present.
Example:
Sr3P2
- Contains 3 atoms Sr (strontium) and 2 atoms P (phosphorus)

6. Chemical Formulas
The ion charge shows what ion each element forms to complete their valence shell of electrons
Al has an ion charge of +3, therefore it loses 3 electrons
Br has an ion charge of -1, therefore it gains one electron
For Al and Br to form a compound Al needs to give away 3 electrons and Br needs to accept them.
But wait!!! Br only needs to accept one, so how does this work??

7. Complete the “Chemical Formulas” worksheet to help you figure out how to determine the chemical formula for an ionic compound.

8. Chemical Formulas
Each Br can accept only 1 electron, so 3 Br atoms are needed to combine with 1 Al
The overall formula needs to show this  AlBr3

9. Chemical Formulas
What would the Ionic Formula be for a compound made of Aluminum and Sulphur?
Al has an ion charge of +3
S has an ion charge of -2

10. For all elements to end up with full valence shells, 2 atoms of Al and 3 of S are required.
Formula = Al2S3

11. Shortcut to write the formula:
Write the symbol and ion charge of the positive ion
Write the symbol and ion charge of the negative ion
Criss-cross the charges and write as subscripts
Reduce numbers (if possible)

12. Examples:
Aluminum sulphide
Al S-2
Al S
Al2S3

13. Examples:
Magnesium Oxide
Mg O-2
Mg O
Mg2O2
REDUCE!!
MgO

14. Assignment:
Complete the practice problems on pages 86 and 87

15. Compounds Containing a Multivalent Metal
Multivalent metals have more than one possible ion charge.
The name must indicate which ion charge is used in the formation of the compound
We use roman numerals to indicate ion charge:
I = 1 VI = 6
II = 2 VII = 7
III = 3 VIII = 8
IV = 4 IX = 9
V = 5 X = 10

16. Compounds Containing a Multivalent Metal
Examples:
V4+ = Vanadium (IV)
Ni3+ = Nickel (III)
Writing formulas is identical to other ionic compounds, simply use the roman numeral to determine the ion charge of the cation!

17. Compounds Containing a Multivalent Metal
Example:
Manganese (IV) sulfide
Mn4+ S2-
Mn2S4
MnS2
** Complete the practice problems on page 89**

18. Compounds Containing a Multivalent Metal
Naming these types of compounds requires an extra step….you must UNCRISSCROSS!!

19. Compounds Containing a Multivalent Metal
Example: Name PdS2
1. Look up the metal on the periodic table and confirm that it is multivalent.
2. Uncrisscross so that the subscripts become charges once again
Pd1S2
Pd2+ S1-

20. Compounds Containing a Multivalent Metal
Check the ion charge of the non-metal to make sure it’s correct. If not, multiply both charges to make it correct.
Pd2+ S1-
- wait!! Sulfur should have an ion charge of -2!!
-to fix this, multiply both ion charges by 2
Pd4+ S2-

21. Compounds Containing a Multivalent Metal
Name the metal, using roman numerals to indicate its ion charge
Palladium (IV)
Name the non-metal, swapping ending for –ide.
Palladium (IV) Sulphide

22. Compounds Containing a Multivalent Metal
Name these compounds:
SnCl2
PbS2
Complete the practice problems on page 90!

23. Polyatomic Ions
Some special molecules lose or gain electrons as a group
These ionic molecules are called polyatomic ions

24. Polyatomic Ions
You can recognize that a compound has a polyatomic ion in it because it will be made up of MORE THAN 2 TYPES OF ATOMS!
Naming:
Example: NaNO3
Name the cation
Sodium
2. Name the polyatomic ion
Nitrate
Sodium Nitrate

25. Example: Calcium Bicarbonate
Writing Formulas
Write the symbol and ion charge for both parts of the name
Criss Cross the charges
- put brackets around the polyatomic ion if necessary
3. Reduce if possible
Example: Calcium Bicarbonate
Ca2+ HCO3-
Ca HCO3
Ca(HCO3)2

26. Complete the practice problems on page 91 Complete Check Your Understanding page 95 #1-6