1. Breakdown of Topics
Chemical formulas, Relation to Type of Substances, “Formula Unit” concept, and Visual connections (related to Tro, 3.3, 3.4)
Ionic Compound Formulas
Difference between ions and ionic compounds (formula writing)
The “neutrality principle” concept
Naming of Compounds (not elements!)
Ionic Compounds
Binary Molecular Compounds
Acids

2. I. Chemical Formulas Revisited
Related to “nanoscopic pictures”
Every substance is composed of “basic units”
If sample A has “more of” a substance than sample B, it has more “basic units” of that substance:
Sample B of NO2
Sample A of NO2
Every substance has a single chemical formula that represents its “basic unit”
One “unit” of any substance can be called a “formula unit”! (Here, one molecule = 1 formula unit)

3. Reminder …these do not have a chemical formula
Monatomic
Molecular
Ionic
…these do not have a chemical formula
Each of these has a chemical formula…
Quick quiz:
How many substances are in the box?
Note: there are four kinds of substances…
…and their formulas “tell you” which is which!...
How many chemical formulas would be needed to describe the matter in the box?
Ans. 2 (e.g., CS2 & O3)

4. Fig. 3.4 Four types of substances—relationship to nanoscopic entities & chemical formulae
Chapter 3, Figure 3.4
A Molecular View of Elements and Compounds
Look closely at the different formulas—can tell the difference between an element and a compound? A monatomic vs polyatomic element?

5. How do you recognize a monatomic element from a formula?
single element symbol with no subscript
Fe, Co, He
One “unit” of the substance. The chemical formula represents one unit of a substance.
Unit = atom
Fe (s)
He (g)
Chemical formula
State designation

6. How do you recognize a molecular element from a formula?
A single element symbol with a subscript
S8, N2, P4, C60
One “unit” of the substance. The chemical formula represents one unit of a substance.
Unit = molecule
C60 (s)
H2 (g)
Chemical formula
C60 Image: courtesy of J. Lauher's Fullerene Structure Library

7. How do you recognize a molecular compound from a formula?
more than one element symbol ( compound)
first one is NOT that of a metallic element (exception later) ( molecular)
CH4, SO2, SO3, P4O10
One “unit” of the substance. The chemical formula represents one unit of a substance.
Unit = molecule
CH4 (s)
SO3 (g)
Chemical formula

8. How do you recognize an ionic compound from a formula?
more than one element symbol ( compound)
first one IS that of a metal (exception later) ( ionic)
NaCl, FeCl3, CuSO4, Na3PO4
The chemical formula still represents one unit of a substance, but it is not a separate grouping as in molecular substances.
Basic units are “ions”…
…but THE “unit” is a specific grouping of ions (indicated by the formula)
NaCl (s)
FeCl3 (s)
…what do you call “it” (the “unit”)?
Chemical formula
…a “formula unit”!

9. Formula units (FU) are the “basic units” of ionic compounds
A formula unit is an amount of a substance. You can have:
one FU of NaCl or
Two FU of NaCl or
25,333 FU of NaCl or
1.56 x 1021 FU of NaCl
Quick Quiz: Can you have:
4.3 FU of NaCl?
0.5 FU of CO2?
NO! A FU is a “unit” of a substance—you cannot have a “fraction” of one! You can only have a whole number of them.
Just like you can have:
one molecule of CO2 or
Two molecules of CO2 or
25,333 molecules of CO2 or
1.56 x 1021 molecules of CO2

10. Formula Unit is just another term for “basic unit” of any substance
Most chemists use the term “formula unit” only with ionic compounds (b/c you can use “atom” or “molecule” for the other kinds of substances)
However, I often use the term with monatomic elements or molecular substances as well
− e.g., 15 FU of CO2 means 15 molecules of CO2
− e.g., 432 FU of Fe means 432 atoms of Fe
“More” of a substance means more “formula
units” of it!

11. How many FUs of each substance are present?
___ FU of Fe 7
___ FU of He 6
___ FU of CH4 8
___ FU of SO3 5
___ FU of N2 7
___ FU of NaCl 12
___ FU of FeCl3 4

12. Click to add notes

13. II. Ion and Ionic Compound Formulas
The chemical formula of any ion MUST show the charge as a superscript on the right:
Na+, Ru3+, Ca2+, O2-, NO2-, PO43-
Ions are not “compounds” (they’re not “substances”!)
The chemical formula of any ionic compound MUST show NO CHARGES AT ALL!
Na2O, Ru2O3, Ca(NO2)2, Na3PO4
NOTE: Your only clue that a formula of a compound represents an ionic compound is noticing the metal in front (exception later)

14. Subscripts of ions tell you how many (of each) are in 1 FU
Formula Na2O Ru2O3 Ca(NO2)2 Na3PO4
1 FU contains exactly:
Two Na+ ions and one O2- ion
Two Ru3+ ions and three O2- ions
One Ca2+ ion and two NO2- ions
Three Na+ ions and one PO43- ion
NOTE: Parentheses are used ONLY if more than one of a polyatomic ion is present in one FU.

15. What determines the number of each ion in a formula unit of an ionic compound?
The charges on the cation and anion that make it up!
The oppositely charged ions will come together in the ratio that makes each formula unit electrically neutral
“neutrality principle”

16. Neutrality Principle A formula unit is always NEUTRAL overall
The grouping of cations and anions must be neutral overall!
Total positive charge = total negative charge
Consistent with compound formula (no charge!)
Formula
Na2O: Na+ Na+ O2-  (+1) + (-2) = 0
Na3PO4 Na+ Na+ Na+ PO43-
 3(+1) + 1(-3) = 0

17. Test: Use Neutrality Principle to Determine the Charge on an Ion
Assume you know that O forms 2- ions (i.e. “O” = O2-) What is the charge on the Ru ions in Ru2O3?
Ru?
O2-
1 FU of compound; net charge must be zero
ANS: +3
3 x 2- = -6 for the three O2- ions.
The two Ru ions must add up to +6
2 x ___ = +6 +3
charge per ion

18. Test: Use Neutrality Principle to Determine the Charge on an Ion
What is the charge on the Pb ions in PbO2?
Pb?
O2-
1 FU of compound; net charge must be zero
ANS: +4
2 x 2- = -4 for the two O2- ions.
The one Pb ion must add up to +4
**If you said +2 then you are using a shortcut instead of thinking about the MEANING of the subscripts! They are NOT “charges”—they represent the number of ions in 1 FU**

19. Use the neutrality principle to determine the formula for an ionic compound
Ions Fe3+ & Br- Ti4+ & S2- Ca2+ & PO43- NH4+ & SO42-
Formula:
FeBr3
TiS2
Ca3(PO4)2
(NH4)2SO4
The exception I mentioned earlier!
Why do you need this skill?
To determine the chemical formula from the name!
“Cobalt(III) carbonate” is composed of cobalt(III) ions (Co3+) and carbonate ions (CO32-):
Formula is: _________
Co2(CO3)3

20. III.A Naming Ionic Compounds
Cation Name + Anion Name That’s it!!!
Hard part: names of the ions!

21. Cations that always have the same charge (can memorize)
Na+
Li+ K+
Rb+
Cs+
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
Al3+
Zn2+
Ag+
Ra2+
1) Monatomic, Type I cations (in this class)
Fr+
One Polyatomic cation (the “exception”):
NH4+, ammonium ion

22. Cations with more than one possible charge (Type II) need a Roman Numeral
Any metal cation other than those on previous slide!
Any transition metal ion other than Ag+ or Zn2+
Any metal ion directly under the staircase other than Al3+
Must use neutrality principle to figure out the charge (if not given to you)!
Write the charge as a Roman numeral in parentheses

23. Type II Cation Examples
Fe3+ is iron(III) ion; Fe2+ is iron(II)
Pb4+ is lead(IV) ion; Pb2+ is lead(II)
Cu+ is copper(I) ion; Cu2+ is copper(II)
Cr6+ is chromium(VI) ion; Cr3+ is chromium(III)
But: Ag+ is just silver ion (Type I)
Zn2+ is just zinc ion (Type I)

24. Anions—Preliminary Comment
It will be much easier to learn anion names if you know these nonmetal elements’ symbols and names (next slide). 24

26. Anions—Three Endings (-ide, -ate, and –ite)
-ides
Monatomic
Use Periodic Table:
P3-
Phosphide
Two polyatomic ones to memorize
CN- (cyanide); OH- (hydroxide)

27. Anions (continued) -ates Polyatomic, contain oxygen (“oxoanions”)
Learn the four “core ions” first (next slide)
Then others from them…

28. Some “–ate” ions to learn first…
NO3- nitrate
SO sulfate
PO phosphate
CO carbonate
…and second
(**Note that these are all analogous to nitrate**):
ClO chlorate
BrO bromate
IO iodate

29. Mnemonic-- “Poconoso”
charge (negative)
PO CO NO SO
# oxygen atoms
PO CO NO3- SO42-

30. “Hydrogen ___” ions come from adding H+ to an oxoanion

31. What’s the name of HS- ion?
Ans: hydrogen sulfide (not on sheet!)

32. Anions (continued) -ites One less oxygen than “ate” counterpart
Sulfate → sulfite (SO42- → SO32-)

33. “-ites” come from “-ates”!

34. “Per-” and “Hypo” in sets of four
ClO4- perchlorate (from “hyper”)
ClO chlorate
ClO chlorite
ClO- hypochlorite (from “hypo”)
Summary: Prefixes of “per” (4 O’s) and “hypo” (1 O) are added in cases where there are four “versions” instead of two.

35. A few additional anions don’t follow any obvious pattern (memorize)
MnO4- permanganate (analogous to ClO4-)
C2H3O2- acetate
CrO chromate
Cr2O dichromate

36. Examples!!!
See handout (and board for detailed solutions to Q’s below):
BaCO3
Fe(NO3)2
PbCl4
AgClO
barium carbonate
iron(II) nitrate
lead(IV) chloride
silver hypochlorite
Fe(OH)2
iron(II) hydroxide _________________
magnesium phosphite _____________
Mg3(PO3)2

37. IIIB. Naming Binary Molecular Compounds
“binary”-two different kinds of atoms (2 different elements’ symbols in formula)
“molecular”- basic units are molecules
Molecules are made of atoms
Atoms are neutral
What’s the ratio of atoms in a molecule?
NO SINGLE “ANSWER” It varies! (no “neutrality” principle to “restrict” b/c atoms already neutral!)
CO and CO2; NO, N2O, NO2,, N2O4, etc. all exist!
Later, we’ll explore models of bonding…

38. Naming Binary Molecular Compounds (continued)
Thus, prefixes are needed to let the reader know what that ratio (and exact composition of a FU) is!
Note: NO2 and N2O4 mean different things even though ratio is the same!
General “Recipe” for name:
1st Element Name + 2nd element’s stem + -ide
Add prefixes as needed to the element or element stem
NOTE: “Mono” is left off 1st Element Name

39. Examples N2O: dinitrogen monoxide NO2: nitrogen dioxide
NO: nitrogen monoxide
N2O4: dinitrogen tetroxide
P4O10: tetraphosphorus decoxide
CF4: carbon tetrafluoride
SCl6: sulfur hexachloride
(start at 3:20)
OR (better yet) Tro’s video [see Mastering practice]

40. The Prefixes You Need to Know
1: mono (only used on second element)
2: di
3: tri
4: tetra
5: penta
6: hexa
7: hepta
8: octa
9: nona
10: deca

41. Comment
Do not confuse the –ide ending with the “ides” of actual anions!!!!!
There are NO IONS in binary molecular compounds, even though the “ide” may make it sound as such!
CCl4, carbon tetrachloride does NOT contain any chloride ions.
I wish that the naming system were completely different for molecular compounds (no “–ides”), but I don’t get to decide! 
(start at 3:20)

42. Examples SO3 Sulfur trioxide __________________
B2F6 __________________________
SrF2 __________________________
diboron hexafluoride
strontium fluoride (no “di” here!**)
** The last one is ionic, not molecular! Make sure to identify “ionic” vs. “molecular” before you begin to name a substance!!

43. IIIC. Acids—A subset of molecular compounds
Molecular compounds that yield ions when dissolved in water!? (more later)
Always have H written first
Imagine making any acid by adding H+‘s to any anion in order to make a neutral formula unit.
The ENDING of the anion determines the name of the acid:
Ide → hydro ___ic acid
Ate → ____ic acid
Ite → ____ous acid
(start at 1:35)

44. Examples H2S Hydrosulfuric acid _________________
Chloric acid _______________________
Hypochlorous acid _________________
H3PO3 __________________________
HNO3 ___________________________
HNO2 ___________________________
HCN ____________________________
H2SO4
HClO3
HClO
phosphorous acid
nitric acid
nitrous acid
hydrocyanic acid

45. From Practice Handout
*You don’t need to memorize oxalate

46. For some web practice
NOTE: This site does NOT do Type II metals at all!