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Formulas Describe Compounds
water = H2O two atoms of
hydrogen and 1 atom of oxygen
Nomenclature
table sugar = C12H22O11 12 atoms
of C, 22 atoms of H and 11 atoms O
2
Molecules with
Polyatomic Ions
Order of Elements in a Formula
• metals written first
NaCl
symbol of the polyatomic
ion called nitrate
• nonmetals written in order from
Table 1(below)
CO2
are occasional exceptions for
historical or informational reasons
H2O, but NaOH
Table 1
Order of Listing Nonmetals
in Chemical Formulas
C P N H S
I Br Cl O F
symbol of the polyatomic
ion called sulfate
Mg(NO3)2
CaSO4
compound called
magnesium nitrate
compound called
calcium sulfate
implied “1” subscript
on magnesium
parentheses to group two NO3’s
implied “1” subscript
on calcium
no parentheses for one SO4
3
Molecules with
Polyatomic Ions
subscript indicating
two NO3 groups
CaSO4
compound called
magnesium nitrate
compound called
calcium sulfate
implied “1” subscript
on nitrogen, total 2 N
stated “3” subscript
on oxygen, total 6 O
Classifying Materials
• atomic elements = elements whose
particles are single atoms
• molecular elements = elements whose
particles are multi-atom molecules
• molecular compounds = compounds
whose particles are molecules made
of only nonmetals
• ionic compounds = compounds whose
particles are cations and anions
no subscript indicating
one SO4 group
Mg(NO3)2
implied “1” subscript
on sulfur, total 1 S
stated “4” subscript
on oxygen, total 4 O
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5
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Molecular Elements
• Certain elements occur as 2 atom molecules
• Rule of 7’s
Molecular Compounds
 there are 7 common diatomic elements
 find the element with atomic number 7, N
 make a figure 7 by going over to Group 7A, then down
 don’t forget to include H2
VIIA
H2
N2
7
P4
O2
F2
S8
Cl2
• two or more
nonmetals
• smallest unit is a
molecule
Br2
I2
7
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Molecular View of
Elements and Compounds
Ionic Compounds
• metals + nonmetals
• no individual
molecule units, instead
have a 3-dimensional
array of cations and
anions made of
formula units
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Classify each of the following as either an
atomic element, molecular element, molecular
compound or ionic compound
• aluminum, Al
• aluminum chloride, AlCl3
• chlorine, Cl2
• acetone, C3H6O
• carbon monoxide, CO
• cobalt, Co
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10
Classify each of the following as either an
atomic element, molecular element, molecular
compound or ionic compound
• aluminum, Al = atomic element
• aluminum chloride, AlCl3 = ionic compound
• chlorine, Cl2 = molecular element
• acetone, C3H6O = molecular compound
• carbon monoxide, CO = molecular compound
• cobalt, Co = atomic element
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Formula-to-Name
Step 1
Formula-to-Name
Step 2
Is the compound one of the
exceptions to the rules?
What major class of compound is it?
Ionic or Molecular
•H2O = water, steam, ice
•NH3 = ammonia
Major Classes
• Ionic
 metal + nonmetal
Formula-to-Name
Step 3
 metal first in formula
 Binary Ionic
 compounds with polyatomic ions
• Molecular
What major subclass of compound is it?
Binary Ionic, Ionic with Polyatomic Ions,
Binary Molecular,
Binary Acid, Oxyacid
 2 nonmetals
 Binary Molecular (or Binary Covalent)
 Acids – formula starts with H
 though acids are molecular, they behave as ionic when
dissolved in water
 may be binary or oxyacid
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Classifying Compounds
• Compounds containing a metal and a nonmetal =
binary ionic
 Type I and II
Formula-to-Name
Step 4
• Compounds containing a polyatomic ion =
ionic with polyatomic ion
• Compounds containing two nonmetals =
binary molecular compounds
• Compounds containing H and a nonmetal =
binary acids
• Compounds containing H and a polyatomic ion =
oxyacids
Apply Rules for the Class and Subclass
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Formula-to-Name
Rules for Ionic
Monatomic Nonmetal Anion
• determine the charge from position on the
Periodic Table
• to name anion, change ending on the element
name to –ide
• Made of cation and anion
• Name by simply naming the ions
If cation is:
Type I metal = metal name
Type II metal = metal name(charge)
Polyatomic ion = name of polyatomic ion
If anion is:
Nonmetal = stem of nonmetal name + ide
Polyatomic ion = name of polyatomic ion
4A = -4
5A = -3
6A = -2
7A = -1
C = carbide
N = nitride
O = oxide
F = fluoride
S = sulfide
Cl = chloride
Si = silicide P = phosphide
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20
Determine if the following metals are Type I
or Type II. If Type I, determine the charge on
the cation it forms.
Metal Cations
• Type I
 metals whose ions can only have one
possible charge
 IA, IIA, (Al, Ga, In)
 determine charge by position on the
Periodic Table
 IA = +1, IIA = +2, (Al, Ga, In = +3)
• Type II
 metals whose ions can have more than How do you know a
one possible charge
metal cation is Type II?
 determine charge by charge on anion
its not Type I !!!
•
•
•
•
•
lithium, Li
copper, Cu
gallium, Ga
tin, Sn
strontium, Sr
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Determine if the following metals are Type I
or Type II. If Type I, determine the charge on
the cation it forms.
•
•
•
•
•
lithium, Li
copper, Cu
gallium, Ga
tin, Sn
strontium, Sr
Type I
Type II
Type I
Type II
Type I
+1
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Type I Binary Ionic Compounds
• Contain Metal Cation + Nonmetal Anion
• Metal listed first in formula & name
1. name metal cation first, name nonmetal anion
second
2. cation name is the metal name
3. nonmetal anion named by changing the ending
on the nonmetal name to -ide
+3
+2
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Type II Binary Ionic Compounds
•
•
Examples
Contain Metal Cation + Nonmetal Anion
Metal listed first in formula & name
•
•
•
•
•
•
•
1. name metal cation first, name nonmetal anion second
2. metal cation name is the metal name followed by a
Roman Numeral in parentheses to indicate its charge
 determine charge from anion charge
 Common Type II cations in Table 3.3 (pg. 97)
3. nonmetal anion named by changing the ending on the
nonmetal name to -ide
LiCl = lithium chloride
AlCl3 = aluminum chloride
PbO = lead(II) oxide
PbO2 = lead(IV) oxide
Mn2O3 = manganese(III) oxide
ZnCl2 = zinc(II) chloride or zinc chloride
AgCl = silver(I) chloride or silver chloride
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Compounds Containing
Polyatomic Ions
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Fixed Charge Metals and Nonmetals
IA
IIA
• Polyatomic ions are single ions that contain
more than one atom
• Name any ionic compound by naming cation
first and then anion
Non-polyatomic cations named like Type I and II
Non-polyatomic anions named with -ide
Li+1
IIIA
Be+2
Na+1 Mg+2
Al+3
K+1 Ca+2
Zn+2 Ga+3
Rb+1 Sr+2
VA VIA VIIA
N-3 O-2
F-1
P-3 S-2
Cl-1
As-3 Se-2 Br-1
Ag+1 Cd+2 In+3
Te-2 I-1
Cs+1 Ba+2
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Some Common Polyatomic Ions
Name
acetate
carbonate
hydrogen carbonate
(aka bicarbonate)
hydroxide
nitrate
nitrite
chromate
dichromate
ammonium
Formula
C2H3O2
CO32–
HCO3–
OH–
NO3–
NO2–
CrO42–
Cr2O72–
NH4+
–
Name
Formula
hypochlorite
chlorite
chlorate
perchlorate
sulfate
sulfite
hydrogensulfate
(aka bisulfate)
hydrogensulfite
(aka bisulfite)
ClO–
Patterns for Polyatomic Ions
1. elements in the same column form similar
polyatomic ions
ClO2–
ClO3–
ClO4–
SO42–
SO32–
HSO4
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 same number of O’s and same charge
ClO3- = chlorate
BrO3- = bromate
–
HSO3–
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2. if the polyatomic ion starts with H, the name
adds hydrogen- prefix before name and add
1 to the charge
CO32- = carbonate
HCO3-1 = hydrogencarbonate
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Binary Molecular Compounds
of 2 Nonmetals
Periodic Pattern of Polyatomic Ions
-ate groups
IIIA
IVA
-3
BO3
VA
-2
VIIA
-1
CO3
NO3
-2
SiO3
VIA
-3
PO4
-3
AsO4
1. Name first element in formula first
 use the full name of the element
2. Name the second element in the formula with an -ide
-2
SO4
-2
SeO4
-2
TeO 4
-1
ClO3
-1
BrO3
-1
IO3
 as if it were an anion, however, remember these
compounds do not contain ions!
3. Use a prefix in front of each name to indicate the
number of atoms
a) Never use the prefix mono- on the first element
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Subscript - Prefixes
•
•
•
•
•
•
•
•
•
•
1 = mono 2 = di3 = tri4 = tetra5 = penta6 = hexa7 = hepta8 = octa9 = nona10 = deca-
Acids
• Contain
not used on first nonmetal
H+1
cation and anion
in aqueous solution
• Binary acids have H+1 cation
and nonmetal anion
• Oxyacids have H+1 cation
and polyatomic anion
drop last “a” if name
begins with vowel
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Example – Naming Binary Acids
HCl
Formula-to-Name
Acids
• acids are molecular compounds that often behave
like they are made of ions
• All names have acid at end
• Binary Acids = hydro prefix + stem of the name of
the nonmetal + ic suffix
• Oxyacids
 if polyatomic ion ends in –ate = name of polyatomic
ion with –ic suffix
 if polyatomic ion ends in –ite = name of polyatomic ion
with –ous suffix
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1. Is it one of the common exceptions?
H2O, NH3, CH4, NaCl, C12H22O11 = No!
2. Identify Major Class
first element listed is H,
Acid
3. Identify the Subclass
2 elements,
Binary Acid
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Sample - Naming Binary
Acids – HCl
Example – Naming Oxyacids
H2SO4
4. Identify the anion
1. Is it one of the common exceptions?
H2O, NH3, CH4, NaCl, C12H22O11 = No!
2. Identify Major Class
Cl = Cl-, chloride because Group 7A
5. Name the anion with an –ic suffix
Cl- = chloride
chloric
6. Add a hydro- prefix to the anion name
first element listed is H,
hydrochloric
Acid
3. Identify the Subclass
7. Add the word acid to the end
3 elements in the formula,
Oxyacid
hydrochloric acid
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Example – Naming Oxyacids
H2SO3
Example – Naming Oxyacids
H2SO4
4. Identify the anion
1. Is it one of the common exceptions?
H2O, NH3, CH4, NaCl, C12H22O11 = No!
2. Identify Major Class
SO4 = SO42- = sulfate
5. If the anion has –ate suffix, change it to –ic. If the
anion has –ite suffix, change it to -ous
SO42- = sulfate
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sulfuric
first element listed is H,
6. Write the name of the anion followed by the word acid
sulfuric acid
(kind of an exception, to make it sound nicer!)
Acid
3. Identify the Subclass
3 elements in the formula,
Oxyacid
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Example – Naming Oxyacids
H2SO3
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Formula-to-Name Flow Chart
4. Identify the anion
SO3 = SO32- = sulfite
5. If the anion has –ate suffix, change it to –ic. If
the anion has –ite suffix, change it to -ous
SO32- = sulfite
sulfurous
6. Write the name of the anion followed by the
word acid
sulfurous acid
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Writing the Formulas from the Names
•
Name – to – Formula
•
For binary molecular compounds, use the
prefixes to determine the subscripts
For Type I, Type II, Ternary Compounds
and Acids
1. Determine the ions present
2. Determine the charges on the cation and anion
3. Balance the charges to get the subscripts
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Example – Binary Molecular
dinitrogen pentoxide
Compounds that Contain Ions
• compounds of metals with nonmetals are made
of ions
• Identify the symbols of the elements
nitrogen = N
oxide = oxygen = O
• Write the formula using prefix number for
subscript
di = 2, penta = 5
N2O5
metal atoms form cations, nonmetal atoms for anions
• compound must have no total charge, therefore
we must balance the numbers of cations and
anions in a compound to get 0 charge
• if Na+ is combined with S2-, you will need 2 Na+
ions for every S2- ion to balance the charges,
therefore the formula must be Na2S
45
Write the formula of a compound made from
aluminum ions and oxide ions
Writing Formulas for
Ionic Compounds
1.
2.
3.
4.
5.
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1.
Write the symbol for the metal cation and its charge
Write the symbol for the nonmetal anion and its charge
Charge (without sign) becomes subscript for other ion
Reduce subscripts to smallest whole number ratio
Check that the sum of the charges of the cation cancels
the sum of the anions
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2.
3.
4.
5.
Write the symbol for the metal
cation and its charge
Write the symbol for the
nonmetal anion and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
Al+3 column IIIA
O2- column VIA
Al+3 O2Al2 O3
Al = (2)∙(+3) = +6
O = (3)∙(-2) = -6
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Practice - What are the formulas for
compounds made from the following ions?
Practice - What are the formulas for
compounds made from the following ions?
• potassium ion with a nitride ion
• K+ with N3-
K3N
• calcium ion with a bromide ion
• Ca+2 with Br-
CaBr2
• aluminum ion with a sulfide ion
• Al+3 with S2-
Al2S3
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Example – Ionic Compounds
manganese(IV) sulfide
1.
2.
3.
4.
5.
Write the symbol for the cation
and its charge
Write the symbol for the anion
and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
Example – Ionic Compounds
Iron(III) phosphate
1.
Mn+4
S2Mn+4 S2-
2.
Mn2S4
3.
4.
MnS2
Mn = (1)∙(+4) = +4
S = (2)∙(-2) = -4
5.
Write the symbol for the cation
and its charge
Write the symbol for the anion
and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
Fe+3
PO43Fe+3 PO43- Fe3(PO4)3
FePO4
Fe = (1)∙(+3) = +3
PO4 = (1)∙(-3) = -3
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Example – Ionic Compounds
ammonium carbonate
1.
2.
3.
4.
5.
Write the symbol for the cation
and its charge
Write the symbol for the anion
and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
52
Practice - What are the formulas for
compounds made from the following ions?
NH4+
• copper(II) ion with a nitride ion
CO32NH4+ CO32- (NH4)2CO3
• iron(III) ion with a bromide ion
(NH4)2CO3
NH4 = (2)∙(+1) = +2
CO3 = (1)∙(-2) = -2
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• aluminum ion with a sulfate ion
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Example – Binary Acids
hydrosulfuric acid
Practice - What are the formulas for
compounds made from the following ions?
• Cu2+ with N3-
1.
Cu3N2
2.
• Fe+3 with Br-
3.
FeBr3
4.
• Al+3 with SO42-
5.
Al2(SO4)3
Write the symbol for the cation
and its charge
Write the symbol for the anion
and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
H+
S2H+ S2-
in all acids the
cation is H+
hydro means
binary
H2S
H2S
H = (2)∙(+1) = +2
S = (1)∙(-2) = -2
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Example – Oxyacids
carbonic acid
1.
2.
3.
4.
5.
Write the symbol for the cation
and its charge
Write the symbol for the anion
and its charge
Charge (without sign) becomes
subscript for other ion
Reduce subscripts to smallest
whole number ratio
Check that the total charge of
the cations cancels the total
charge of the anions
H+
CO32-
in all acids the
cation is H+
no hydro means
polyatomic ion
-ic means -ate ion
H+ CO32-
H2CO3
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Practice - What are the formulas for the
following acids?
• chlorous acid
• phosphoric acid
H2CO3
H = (2)∙(+1) = +2
CO3 = (1)∙(-2) = -2
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• hydrobromic acid
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Practice - What are the formulas for the
following acids?
• H+ with ClO2–
HClO2
• H+ with PO43–
H3PO4
• H+ with Br–
HBr
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