Breakdown of Topics
I.
Chemical formulas, Relation to Type of
Substances, “Formula Unit” concept, and
Visual connections (related to Tro, 3.3, 3.4)
II. Ionic Compound Formulas
A. Difference between ions and ionic compounds
(formula writing)
B. The “neutrality principle” concept
III. Naming of Compounds (not elements!)
A. Ionic Compounds
B. Binary Molecular Compounds
C. Acids
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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 A of NO2
Sample B 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) 2
Reminder
…these do not
have a chemical
formula
Each of these
has a chemical
formula…
Quick
quiz:
Monatomic
How many substances are in the box?
How many chemical formulas would
be needed to describe the matter in
the box?
Ans. 2 (e.g., CS2 & O3)
Molecular
Molecular
Ionic
Note: there are four kinds of substances…
…and their formulas “tell you” which is which!...
3
Fig. 3.4 Four types of substances—relationship
to nanoscopic entities & chemical formulae
Look closely at the different formulas—can tell the difference between an
element and a compound? A monatomic vs polyatomic element?
4
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
5
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
6
C60 Image: courtesy of J. Lauher's Fullerene Structure Library
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)
One “unit” of the substance. The chemical
– CH4, SO2, SO3, P4O10
formula represents one unit of a substance.
Unit = molecule
CH4 (s)
SO3 (g)
Chemical
formula
7
How do you recognize an ionic
compound from a formula?
• more than one element symbol ( compound)
• first one IS that of a metal (exceptions 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.
NaCl (s)
FeCl3 (s)
Chemical
formula
Basic units are
“ions”…
…but THE “unit” is
a specific grouping
of ions (indicated
by the formula)
…what do you call
“it” (the “unit”)?
…a “formula unit”!
8
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
• 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
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.
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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!
10
How many FUs of each substance are
present?
7 FU of Fe
___
___
7 FU of N2
6 FU of He
___
8 FU of CH4
___
___
12 FU of NaCl
5 FU of SO3
___
___
4 FU of FeCl3
11
12
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-
• 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 compound formula represents an ionic
compound is noticing the metal in front (exception later)
13
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.
14
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”
15
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
Formula
Na2O:
Na+ Na+ O2-  +1 + (+1) + (-2) = 0
Na3PO4 Na+ Na+ Na+ PO43 3(+1) + 1(-3) = 0
16
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?
1 FU of
O2?
Ru
Ru?
O2O2-
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 ___
+3 = +6
charge per ion
17
Test: Use Neutrality Principle to
Determine the Charge on an Ion
What is the charge on the Pb ions in
PbO2?
1 FU of
2Pb?
O
O2-
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**
18
Use the neutrality principle to determine
the formula for an ionic compound
Ions
Fe3+ & BrTi4+ & S2Ca2+ & PO43NH4+ & SO42-
Formula:
FeBr3
TiS2
Ca3(PO4)2
(NH4)2SO4
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
19
III.A Naming Ionic Compounds
• Cation Name + Anion Name That’s it!!!
• Hard part: names of the ions!
20
Cations that always have the same
charge (can memorize)
Li+ Be2+
1) Monatomic, Type I
cations (in this class)
Na+ Mg2+
Al3+
K+ Ca2+
Rb+ Sr2+
Zn2+
Ag+
Cs+ Ba2+
Fr+ Ra2+
2) One Polyatomic cation: NH4+,
ammonium ion
21
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
22
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)
23
Anions—Preliminary Comment
• It will be much easier to learn anion names
if you know these nonmetal elements’
symbols and names (next slide).
24
25
Anions—Three Endings
(-ide, -ate, and –ite)
• -ides
1) Monatomic
Use Periodic Table:
P3Phosphide
2) Two polyatomic ones to memorize
CN- (cyanide); OH- (hydroxide)
26
Anions (continued)
• -ates
– Polyatomic, contain oxygen (“oxoanions”)
– Learn the four “core ions” first (next slide)
• Then others from them…
27
Some “–ate” ions to learn first…
NO3- nitrate
SO42- sulfate
PO43- phosphate
CO3
2-
carbonate
…and second
(analogous to nitrate):
ClO3-
chlorate
BrO3-
bromate
IO3-
iodate
28
Mnemonic-- “Poconoso”
charge (negative)
3
PO
# oxygen atoms
2
CO
4
3
1
NO
3
2
SO
4
PO43- CO32- NO3- SO4229
“Hydrogen ___” ions come from
adding H+ to an oxoanion
30
What’s the name of HS- ion?
• Ans: hydrogen sulfide
(not on sheet!)
31
Anions (continued)
• -ites
– One less oxygen than “ate” counterpart
– Sulfate → sulfite (SO42- → SO32-)
32
“-ites” come from “-ates”!
33
“Per-” and “Hypo” in sets of four
ClO4-
perchlorate
ClO3-
chlorate
ClO2-
chlorite
ClO-
hypochlorite
(from “hyper”)
(from “hypo”)
• Summary: Prefixes of “per” (4 O’s) and “hypo” (1 O) are
added in cases where there are four “versions” instead
34
of two.
A few additional anions don’t follow
any obvious pattern (memorize)
•
•
•
•
MnO4C2H3O2CrO42Cr2O72-
permanganate (analogous to ClO4-)
acetate
chromate
dichromate
35
Examples!!!
•
•
•
•
•
See handout (and board for detailed solutions to Q’s below):
BaCO3 barium carbonate
Fe(NO3)2 iron(II) nitrate
lead(IV) chloride
PbCl4
silver hypochlorite
AgClO
Fe(OH)2
• iron(II) hydroxide _________________
Mg3(PO3)2
• magnesium phosphite _____________
36
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…
37
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
38
Examples
•
•
•
•
•
•
•
N2O: dinitrogen monoxide
• http://www.youtube.com/w
NO2: nitrogen dioxide
atch?v=NJn76CR70oU
(start at 3:20)
NO: nitrogen monoxide
N2O4: dinitrogen tetroxide
P4O10: tetraphosphorus decoxide
CF4: carbon tetrafluoride
SCl6: sulfur hexachloride
39
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
40
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! 
• http://www.youtube.com/watch?v=NJn76CR70oU (start at 3:20)
41
Examples
SO3
• Sulfur trioxide __________________
diboron hexafluoride
• B2F6 __________________________
strontium fluoride (no “di” here!**)
• SrF2 __________________________
** The last one is ionic, not molecular! Make
sure to identify “ionic” vs. “molecular” before
you begin to name a substance!!
42
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:
•http://www.youtube.com/watch?
– Ide → hydro ___ic acid
– Ate →
____ic acid
– Ite →
____ous acid
v=a5nC2evhUa0
•http://www.youtube.com/watch?
v=LoSLKUN7FQ4 (start at 1:35)
43
Examples
•
•
•
•
•
•
•
•
H 2S
Hydrosulfuric acid _________________
H2SO4
Sulfuric acid ______________________
HClO3
Chloric acid _______________________
HClO
Hypochlorous acid _________________
phosphorous acid
H3PO3 __________________________
nitric acid
HNO3 ___________________________
nitrous acid
HNO2 ___________________________
hydrocyanic acid
HCN ____________________________
44
From Practice Handout
*You don’t need to
memorize oxalate
45
For some web practice
• http://www.stolaf.edu/depts/chemistry/cour
ses/toolkits/125/js/naming/
• http://web.mst.edu/~gbert/names/Aionic.H
TML
– NOTE: This site does NOT do Type II metals at all!
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