1. Chapters 8&9: Names, Formulas, and Oxidation NUmbers

2. Topics in this unit:
Binary Ionic Compounds of Metals with Fixed Charges
Formulas of Ionic Compounds: The criss-cross method
Binary Compounds of Cations with Variable Charges: Stock System
Polyatomics
Names and Formulas of Covalent (Nonmetal) Compounds
Acids
Hydrates
Oxidation Numbers

3. Binary Compounds of Metals with Fixed Charges
Name the cation (metal) first, then the anion (nonmetal)
Use the cation’s name directly from the periodic table (eg. Ca+2 is Calcium)
Name the anion using the root of the element’s name plus the suffix “ide” (eg. S-2 would be Sulfide)
Examples:
CaS would be Calcium Sulfide
Na2O would be Sodium Oxide
Potassium Chloride would be KCl

4. Practice
Name the Following Compounds:
BaCl2
ZnF2
Ag2S
AlBr3

5. Practice Name the Following Compounds: BaCl2 = barium chloride
ZnF2 = zinc fluoride
Ag2S = silver sulfide
AlBr3 = aluminum bromide

6. Formulas of Ionic Compounds: The Criss-Cross Method
Ionic compounds have to combine so that the positive charges are balanced out by the negative charges.
To figure out the ratios of elements, we can use the criss-cross method
Step 1: write the symbols for the ions and their charges as superscripts.
Step 2: criss-cross the values of the charges, not the signs, so that they become subscripts in the formulas
Step 3: make sure the subscripts are in the lowest whole number ratio

7. Formulas of Ionic Compounds: The Criss-Cross Method Example
What is the formula for Sodium sulfide?
Sodium ion = Na+1 Sulfide ion = S-2
Na+1 S-2
Final formula = Na2S1 or Na2S

8. Practice Write the formulas of the following ionic compounds:
Magnesium chloride
Lithium Sulfide
Nickel Oxide
Tungsten Nitride
Sodium Fluoride

9. Practice Write the formulas of the following ionic compounds:
Magnesium Chloride = MgCl2
Lithium Sulfide = Li2S
Nickel Oxide = NiO
Tungsten Nitride = WN2
Sodium Fluoride = NaF

10. Binary Compounds of Cations with Variable Charges: The Stock System
Named for German chemist Alfred Stock
Cations (metals) involved have multiple charges
Anion has fixed charge
Uses roman numerals in parentheses to show the cation’s charge
Example: FeCl2 is iron(II) chloride; FeCl3 is iron (III) chloride

11. The Stock System Name the cation’s element first
Determine the charge by multiplying the anion’s charge by it’s subscript; then divide this by the cation’s subscript
Example 1: Name CuCl2
Chloride anion’s charge is -1 times it’s subscript 2 equals 2 (Ignore sign of -2)
Divide by Copper’s subscript of 1 equals 2
The result is Copper(II) chloride

12. The Stock System Example 2: Name Fe2O3
Oxide anion’s charge is -2 times it’s subscript 3 equals -6
Divide by Iron’s subscript of 2 equals 3
The result is iron(III) oxide
Example 3: Write the formula for manganese(IV) oxide
The cation’s charge is given from the formula +4
Oxide’s charge is -2
Using the criss-cross method we first get Mn2O4,but this is not in the lowest ratio. So we divide each subscript by 2.
The result is MnO2

13. Polyatomics
Polyatomic ions can bond with metals that have fixed or variable charges.
When more than one polyatomic ion is required, parentheses must be used around the polyatomic
Example 1: Fe(NO3)2
Decide if the cation has a variable charge (iron does so you must determine the roman numeral)
NO3 has a -1 charge so iron must be +2
The name is iron(II) nitrate

14. Polyatomics Example 2: Fe(OH)3 Example 3: Aluminum Phosphate
Determine the charge of iron: Hydroxide is -1 so iron must be +3
The compound is iron(III) hydroxide
Example 3: Aluminum Phosphate
Aluminum is a fixed-charge of +3
Phosphate ion is PO4-3
The formula is AlPO4
Example 4: Ammonium Sulfate
Ammonium is a polyatomic cation NH4+
Sulfate is SO4-2
The formula is (NH4)2SO4

15. Names and Formulas of Covalent (Nonmetal) Compounds
Name the first element: if there are two or more, add a prefix to match the subscript
Name the second element also using a prefix to match the subscript (including “mono-” for one). Change the ending to “ide”
Number
Prefix 1
Mono 6
Hexa 2 Di 7
Hepta 3
Tri 8
Octa 4
Tetra 9
Nona 5
Penta 10
Deca

16. Names of Nonmetal Compounds: Examples
Example 1: N2O
Subscript for 2 is “di-” so it is dinitrogen
Subscript for O is 1 so the name is dinitrogen monoxide
Example 2: N2O5
Subscript for nitrogen is 2 so it is dinitrogen
Subscript is 5 for oxygen or pentaoxide
The name is dinitrogen pentaoxide (pentoxide is also acceptable)
Example 3: What is the formula for triphosphorus hexabromide?
Phosphorus is P and tri means there’s 3 P atoms
Bromine is Br and hexa means there’s 6 Br atoms
The formula is P3Br6 (notice we don’t reduce the subscripts)

17. Practice: Covalent Compounds
Name the following covalent compounds: CO
P2O4
PCl3
Write formulas for the following covalent compounds:
Antimony tribromide
Xenon hexafluoride
Diphosphorus decasulfide

18. Practice: Covalent Compounds
Name the following covalent compounds:
CO = carbon monoxide
N2O4 = dinitrogen tetroxide
PCl3 = phosphorus trichloride
Write formulas for the following covalent compounds:
Antimony pentabromide= SbBr5
Xenon hexafluoride = XeF6
Diphosphorus decasulfide = P2S10

19. Acids
Acids are a special type of ionic compound that forms when certain polar molecules dissolve in water
The formulas typically have an H in front
Ex: HCl, H3PO4
The cation is always H+1, so the criss-cross rule still applies for writing formulas
Ex: What acid forms when hydrogen bonds with the sulfate ion?
Hydrogen ion = H+1 sulfate = SO42-
The formula is H2SO4
There are two types of acids, binary and ternary (oxyacids)

20. Binary Acids
Binary acids are hydrogen with a non-metal (Examples: HCl, HF, HBr, HI)
“hydro-” STEM “-ic” is used (STEM comes from the anion)
The word acid is added at the end
Examples:
HCl is hydrochloric acid (STEM is chlor)
HF is hydrofluoric acid
HBr is hydrobromic acid

21. Oxy (Ternary) Acids Contains hydrogen and a polyatomic ion
Change the “ate” ending to “ic” and the “ite” ending to “ous” and add the word acid
Polyatomic ion that ends in “ate”
STEM –ic acid
Example HClO3 = chloric acid
H2SO4 = sulfuric acid
Polyatomic ion that ends in “ite”
STEM –ous acid
Example HClO2 = chlorous acid
H3PO3 = phosphorous acid

22. Oxy (Ternary) Acids Polyatomic ion with prefix “hypo”
Hypo- STEM –ous acid
Example HClO hypochlorous acid
Polyatomic ion with prefix “per”
Per- STEM –ic acid
Example HClO4 perchloric acid

23. Hydrates Ionic compounds that have water in them
General Formula AB . xH2O
Name the compound (AB) and identify the number of water molecules present (x equals the coefficient) with a prefix
Examples:
CuSO4 . 5 H2O is copper(II) sulfate pentahydrate
MgSO4 . 9 H2O is magnesium sulfate nonahydrate

24. Oxidation Numbers: The Rules
All free uncombined elements have an oxidation number of zero (In diatomic elements like F2, each fluorine’s oxidation number is 0)
Hydrogen has an oxidation number of +1
Exception: when combined with metals, H’s oxidation number is -1
Oxygen has an oxidation number of -2
Exception #1: In peroxide (O22-) the oxidation number is -1
Exception # 2: When oxygen bonds with fluorine (OF2) it is +2 because fluorine is more electronegative

25. Oxidation Numbers: The Rules
The alkali metals (group 1A) have an oxidation state of +1
The alkaline earth metals (group 2A) have an oxidation state of +2
The oxidation number of Aluminum (Al) is always +3
The halogens (group 7A) have an oxidation state of −1 (except when they are bonded to oxygen or with another halogen)

26. Oxidation Numbers: The Rules
In a neutral molecule, the sum of the oxidation numbers of all of the atoms must be zero. 
Ex.  In H2O, each hydrogen is +1 and the oxygen is -2.  So, (2 x +1) + (-2) = 0. 
In a polyatomic ion, the sum of oxidation numbers of all the elements in the ion must be equal the net charge of the ion. 
Ex.  In the polyatomic ion known as hydroxide (OH-), the oxygen is -2 and the hydrogen is +1.  So, (-2) + (+1) = -1, the same as the charge on the hydroxide ion (OH-)

27. Oxidation Number Examples
What is the oxidation number of Na in Na2O?
O is -2; the two Na must be +1 each
What is the oxidation number of Cl in ClO¯?
The O is -2, but since a -1 must be left over, then the Cl is +1
What is the oxidation number for each element in KMnO4?
K = +1; O = -2 Mn = +7. There are 4 oxygens for a total of -8, K is +1, so Mn = +7.