1. Names & Formulas of Compounds#3
Naming and Writing Ionic Formulas
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. What is a binary ionic compound?
Binary means “two”
A binary ionic compound is made of 2 elements only…always a metal first and a nonmetal last

3. Some Ionic Compounds with Two Elements
Formula Ions Name
NaCl Na+ Cl- sodium chloride
K2S K+ S2- potassium sulfide
MgO Mg2+ O2- magnesium oxide
CaI2 Ca2+ I- calcium iodide
Al2O3 Al O2- aluminum oxide

4. What you will do…
If given the formula, you will have to determine the correct name
If given the name, you will have to determine the correct formula

5. Get your Periodic Table out and look at it…
Elements in groups 1, 2, and have fixed or set charges when they form ions…you should already have these marked on your table (Group 1 is +1, etc…)
But most transition metals (groups 3-12) AND tin (Sn) and lead (Pb) form multiple ions because of a varying valence
Silver (Ag), Cadmium (Cd), and Zinc (Zn) are the only transition metals that have fixed charges…you must memorize this!!!!!!

6. OUTLINE Silver, Cadmium, & Zinc on your table…write in their charges…OUTLINE Tin & Lead on your table

7. Metals with varying charges
Because most of the metals in groups 3 to 12 and Sn & Pb have multiple charges, when you name them in a compound you must include a Roman Numeral after their name to indicate which ion it is…Pb+2 is called Lead II…Pb+4 is called Lead IV
Remember, Ag, Cd, & Zn have only one charge…they will NEVER need Roman Numerals with their names.

8. Over groups 3-12 write "need roman numerals "
Over groups 3-12 write "need roman numerals ". Under Sn & Pb, write "need roman numerals". Above Ag, Cd, & Zn write "do not need roman numerals". You can abbreviate RN for roman numerals…

9. Another ion to watch for…
Mercury forms two ions
Mercury II is just Hg+2
Mercury I is odd…2 mercury I's will always go in pairs in a compound, so even though they have a +1 charge each, because there are two of them you will use them like this: Hg2+2

10. Writing Formulas when given the name of the compound—
STEP 1. Identify the cation .
Cations are metals. Write down the metal ion and the charge it normally has according to the periodic table. If it has a Roman numeral, that is its charge.
STEP 2. Identify the anion. Anions are nonmetals. Write down the ion and its normal charge.
STEP 3. Balance the charges. Remember that compounds have no charges!!

11. Writing Formulas: Example
Write the formula of potassium sulfide.
STEP 1 Identify the cation and anion.
potassium = K+
sulfide = S2−
STEP 2. Balance the charges.
K S2− K+
2(1+) + 2(1-) = 0
STEP K+ and 1 S2− = K2S

12. Learning Check The correct formula for each of the following is:
A. Copper (I) nitride
1) CuN 2) CuN3 3) Cu3N
B. Lead (IV) oxide
1) PbO2 2) PbO 3) Pb2O4

13. Solution The correct formula is A. Copper (I) nitride
3) Cu3N Need 3Cu+ and N3-
B. Lead (IV) oxide
1) PbO2 Need Pb4+ and 2O2-

14. Naming of Binary Ionic Compounds
To NAME a binary ionic compound
1. Look at the METAL
a. If it's a Group 1, Group 2, or Group 13 metal, OR Ag, Zn, or Cd, just use the name of the metal.
b. If it's a TRANSITION metal from groups 3-12, OR tin (Sn) or lead (Pb) it will need a roman numeral!
2. The negative nonmetal ion (second ion) is named by changing the end of the element name to –ide.
EX: Chlorine becomes chloride
Bromine becomes bromide

15. Names of Some Common Ions
Table 5.3
3A (13)
Copyright © by Pearson Education, Inc. Publishing as Benjamin Cummings

16. Learning Check--practice
Complete the names of the following ions:
Ba2+ Al3+ K+
_________ __________ _________
N3 O2 F
_________ __________ _________
P3 S2 Cl

17. Solution barium aluminum potassium N3 O2 F nitride oxide fluoride
Ba2+ Al3+ K+
barium aluminum potassium
N3 O2 F
nitride oxide fluoride
P3 S2 Cl
phosphide sulfide chloride

18. Learning Check Write the names of the following compounds:
1) CaO ___________
2) KBr ___________
3) Al2O3 ___________
4) MgCl2 ___________

19. Solution Write the names of the following compounds:
1) CaO calcium oxide
2) KBr potassium bromide
3) Al2O3 aluminum oxide
4) MgCl2 magnesium chloride

20. Naming a compound that has a transition metal in it…
To name Cr2O3, or any other compound that contains a metal with a variable charge
Always start with the anion. It has a fixed charge.
O is always (2-) and there are 3 of them. 3 x (-2) = -6.
Therefore, the metal portion must have a total charge of +6 to balance the compound
2. Divide the + charge of metal by the number of metal ions: +6 ÷ 2 = +3
3. Name the cation by the element name and use a
Roman numeral in parenthesis to show its charge.
Cr3+ = chromium(III)
4. Write the name of the anion with -ide ending.
chromium (III) oxide = Cr2O3

21. Learning Check Select the correct name for each. A. Fe2S3
1) iron sulfide
2) iron(II) sulfide
3) iron (III) sulfide
B. CuO (Careful! Remember oxygen’s charge!)
1) copper oxide
2) copper(I) oxide
3) copper (II) oxide

22. Solution Select the correct name for each. A. Fe2S3
3) iron (III) sulfide Fe3+ S2-
B. CuO
3) copper (II) oxide Cu2+ O2-
Note: Because Cu and O both have the same charge, the formula is reduced to a 1:1 ratio
Cu2O2 = CuO