1. Ionic Compounds: Writing Formulas and Names
Formula Units

2. Empirical Formulas
Give the smallest whole-number ratio of elements in the compound.
Ionic compounds have empirical formulas only.

3. Identify the empirical formulas
H2O
H2O2
CaF2
NaCl
CH4
C2H6
NiO
FeCl3
Empirical and possibly Molecular
Molecular
Empirical and Ionic
Memory Jogger
Empirical and Ionic
Empirical and possibly Molecular
Molecular
Empirical and Ionic
Empirical and Ionic

4. Formula Unit The simplest ratio of the ions in an ionic compound.
KBr means potassium ions and bromide ions are in a 1-to-1 ratio and is the formula unit.
For ionic compounds, the formula mass is based on the formula unit.

5. Binary Compounds Composed of two elements Positive monatomic metal ion
Negative monatomic nonmetal ion
Monoatomic ion is a one-atom ion.
Note: A binary compound may contain more than 2 ions but only 2 kinds of ions like Al2O3.

6. Oxidation Number or State
Na+1
Charge of a monatomic ion.
Given by right superscript.
Some elements form only 1 ion.
Some elements can form more than 1 ion.
Try to find patterns.
Ca+2
O-2
Fe+2 and Fe+3

7. Oxidation State of Selected Elements
Group 1 ions always +1
Group 2 ions always +2
MOST group 13 ions are +3
Groups 14, 15, 16, and 17 have multiple oxidation states, both positive and negative. (Start with the first ox #)
Transition metals (Group B) can have more than 1 oxidation state but always positive.

8. Writing Formulas for Binary Cmpds
The first rule in writing formulas for ionic compounds is
POSITIVE ION FIRST
But how do you get the subscripts?
We will start by writing formulas from the ions.

9. Writing Formulas for Binary Cmpds
Compounds are electrically neutral – no charge.
Take the number of each kind of ion X the charge on the ion. Sum these terms. Should get 0.
Positive and negative charges must balance out.

10. Equal but Opposite Charges
Na+1 and Cl-1: NaCl +1 + (-1) = 0
Mg+2 and O-2: MgO +2 + (-2) = 0
Al+3 and P-3: AlP (-3) = 0
Rule: Just write the symbols, POSITIVE FIRST!

11. Try a few formulas: Li+1 and I-1 Ca+2 and O-2 Al+3 and N-3 K+1 and F-1
Ba+2 and S-2
LiI
CaO
AlN KF
BaS

12. Criss-Cross Method When the charges don’t cancel out immediately:
Mg+2 and Cl-1, CROSS and DROP!
(Numbers only, forget signs!)
Mg1Cl2 but if the subscript is 1, forget it!
MgCl2 means 1 Mg+2 and 2 Cl-1

13. Check the Math MgCl2 means 1 Mg+2 and 2 Cl-1
(1 X +2) + (2 X -1) = 2 – 2 = 0
The charges add up to zero!

14. Try a few formulas: Ca+2 + Cl-1 Na+1 + O-2 Cs+1 + S-2 Al+3 + Cl-1
Al+3 + Se-2
Mg+2 + F-1
K+1 + N-3
CaCl2
Na2O
Cs2S
AlCl3
Al2Se3
MgF2
K3N

15. Of course, it gets more difficult
Potassium (K) and Fluorine (F)
Zinc (Zn) and Iodine (I)
Sodium (Na) and Oxygen (O)
Magnesium (Mg) and Oxygen (O)
Aluminum (Al) and Oxygen (O)
Calcium (Ca) and Bromine (Br)
Cesium (Cs) and Iodine (I)
Silver (Ag) and Sulfur (S) KF
ZnI2
Na2O
MgO
Al2O3
CaBr2
CsI
Ag2S

16. Naming Binary Ionic Compounds
Always name the metal (the cation or positive ion) first and use its full name.
Write the stem of the nonmetal (the anion or negative ion).
Add the ending “ide” to the nonmetal.

17. Stems of nonmetals Nitr Ox Fluor Phosph Sulf Chlor Arsen Selen Brom
Tellur
Iod
Hydr is the stem for H

18. The First Step in Naming
Look up the positive metal in the periodic table in your reference tables.
If the metal has only one oxidation state (possible charge), it’s easy.
If the metal has more than one oxidation state, there’s an extra step.

19. Metals with one oxidation state
Calcium Oxide
CaO
BaS
AlN
LiCl
Al2Se3
Na2O
K3N
MgF2
Barium Sulfide
Aluminum Nitride
Lithium Chloride
Aluminum Selenide
Sodium Oxide
Potassium Nitride
Magnesium Fluoride

20. Metals with > 1 oxidation state.
Use the formula to figure out which oxidation state the metal ion has.
Ex: Fe can be Fe+2 or Fe+3
Name FeO and Fe2O3. These are two different compounds. You cannot name them iron oxide. Every formula goes with 1 name and vice-versa.

21. FeO and Fe2O3 FeO 1 O which is -2. The Fe must be +2. Name:
Compounds are electrically neutral.
Oxygen is -2.
1 O which is -2.
FeO
The Fe must be +2.
Name:
Iron (II) oxide
The roman numeral II is the charge on the Fe.

22. FeO and Fe2O3 Fe2O3 Compounds are electrically neutral. Oxygen is -2.
Each Fe is +3.
Iron (III) oxide
Each O is -2.
Fe2O3
There are 3 O’s.
3 X (-2) = -6.
Total negative charge.
Total positive charge must be +6.

23. Name the following Hint: Positive Always First
Titanium (III) chloride
TiCl3
Mn2O4
Co2O3
PdBr2
AuCl3
MoN
MnO
TiO
Manganese (IV) oxide
Cobalt (III) oxide
Palladium (II) bromide
Gold (III) chloride
Molybdenum (III) nitride
Manganese (II) oxide
Titanium (II) oxide

24. POLYATOMIC IONS SO42- CO32- PO43- OH-
A group of covalently bonded atoms that carries a charge.
See Table E. May be +’ve or –’ve.
Polyatomic ions have “names.”
Because they are charged, polyatomic ions can form ionic bonds with oppositely-charged ions.
SO CO PO OH-

25. Ternary (or more) Compounds
Contain 3 or more elements (uppercase letters)
Usually have a polyatomic ion
If the polyatomic is +’ ve, it’s bonded to a nonmetal
If the polyatomic is –’ve, it’s bonded to a metal
Once in a while, 2 polyatomics are bonded together.

26. Formulas with polyatomics
What’s the formula for the compound formed from NH4+1 and Cl-1?
The charges add up to zero, so just write the symbols, positive first!
NH4Cl

27. Try a few more: Na+ and OH- NaOH K + and HCO3-1 Mg+2 and CO3-2 KHCO3
Li + and NO3-
NH4 + and CN-
Ca+2 and SO4-2
NaOH
KHCO3
MgCO3
LiNO3
NH4CN
CaSO4

28. These are more challenging:
Mg3(PO4)2
Mg+2 and (PO4)-3
(NH4)+1 and S-2
Al+3 and (NO3)-1
Fe+2 and OH-1
Hg2+2 and SCN-1
Mg+2 and HCO3-
Al+3 and C2O42-
(NH4)2S
Al(NO3)3
Fe(OH)2
Hg2(SCN)2
Mg(HCO3)2
Al2(C2O4)3

29. Some of the most challenging are
Zn(NO3)2
Zinc + Nitrate ion
Magnesium + Hydroxide ion
Lithium + Carbonate ion
Ammonium ion + Bromine
Potassium + Sulfate ion
Calcium + Phosphate ion
Beryllium + Chlorate ion
Ammonium ion + Sulfate ion
Mg(OH)2
Li2CO3
NH4Br
K2SO4
Ca3(PO4)2
Be(ClO3)2
(NH4)2SO4

30. Naming compounds with polyatomics
Polyatomic ions have names, given in Table E.
Naming is parallel to binary naming.
Positive always first.
If +’ve ion is a metal, check to see how many oxidation states it has. If > 1, name has a roman numeral.
If –’ve is polyatomic, 2nd part of name is name of polyatomic. Don’t modify ending.

31. Name the following Sodium hydroxide NaOH KHCO3 LiNO3
CaSO4
Al(NO3)3
Fe(OH)2
CuSO4
CuSCN
Potassium hydrogen carbonate
Lithium nitrate
Calcium sulfate
Aluminum nitrate
Iron (II) hydroxide
Copper (II) sulfate
Copper (I) thiocyanate

32. Summary for Ionic Compounds
Name = metal + stem of nonmetal + ide.
If the metal has more than 1 oxidation state, it has a roman numeral in the name.
Formula: positive first, always.
Compounds are electrically neutral.
Use oxidation states you know, like O, to figure out the oxidation states that have more than 1 possibility.