Molecules,
Compounds, and
Chemical Equations
Chapter 3
Compounds may be ionic or
molecular
 IONIC


COMPOUNDS
generally form between metals and nonmetals
held together by attraction of oppositely charged ions
 MOLECULAR
COMPOUNDS

generally form between nonmetals

held together by covalent chemical bonds
2
Elements & compounds
3
Most elements are atomic, but a few are molecular
4
Some compounds are ionic

An ionic compound (salt) is made of ions held
together by electrostatic forces of attraction
Positively charged ions are called cations
 Negatively charged ions are called anions

The basic unit of a salt is a formula unit
 A formula unit is not a molecule, but the simplest
ratio of cations & anions in the lattice

5
Sodium
Chloride:
an ionic
compound
6
Some substances are molecular

A molecular substance (element or compound) is made of
molecules (atoms joined by covalent bonds)

The basic unit of a molecular substance is a molecule
7
Molecular and ionic
8
Acetic acid contains
2 C, 2 O, and 4 H

Empirical formula



the simplest ratio of atoms
Molecular formula

C2H4O2
the actual number of atoms
Structural formula

CH2O
shows arrangement of atoms
O
||
CH3–C–OH
9
Mass Percent Composition
The mass of one element in a compound
divided by the total mass of the compound,
times 100%
10
Mass Percent Composition

Calculate the mass percent composition of acetic
acid, HC2H3O2
4 1.0079 2 12.011 2 16.00  60.05
g
mol
4 1.0079 
%H 
 100  6.713%
60.05
2 12.011
%C 
 100  40.00%
60.05
2 16.00 
%O 
 100  53.29%
60.05
11
Empirical Formula from Percent
Composition
Use masses given, or assume you have 100 g of
compound, so mass of each element = the
percent given for each
 Convert the mass of each element into moles
 Write a tentative formula based on the moles
calculated for each element
 Divide all subscripts by the smallest value to
convert them to small whole numbers

12
Calculating an Empirical Formula

Analysis of a sample of a brown gas which is an
important air pollutant shows that it contains 2.34 g
of nitrogen and 5.34 g of oxygen. What is the
empirical formula of the gas?
13
Calculating an Empirical Formula

Analysis of a sample of a brown gas which is an
important air pollutant shows that it is 30.47%
nitrogen and 69.53% oxygen by mass. What is the
empirical formula of the gas?
30.47 g N x 1 mol = 2.175 mol N
14.0067 g
 69.53 g O x 1 mol = 4.346 mol O
15.9994 g
 N2.175O4.346
N(2.175/2.175)O(4.3462.175)
 Empirical formula is NO2

N1.000O1.998
14
Finding the Molecular Formula from
the Empirical Formula
Molecular formula = actual number of atoms
combined in the molecule
 Find ratio
true molar mass
empirical molar mass
 Multiply subscripts in empirical formula by ratio

empirical formula is CH & true molar mass is 78 g/mol

78 g/mol
= 6
(12 + 1) g/mol
 Molecular formula C6H6

15
Molecular Formulas

A compound has the empirical formula of NO2. Its
molar mass is determined to be about 92 g/mol.
What is the compound’s molecular formula?
The empirical formula mass is 14 + 2(16) = 46 g/mol
 92 g/mol = 2
46 g/mol
 Molecular formula is N2O4

16
Determining a Formula using
Combustion Analysis
18
20
Combustion Analysis
0.1000 g of a C, H, and O compound is burned in
O2 to yield 0.1953 g CO2 and 0.1000 g H2O
 In a separate experiment, the molar mass is
determined to be about 90 g/mol
 Calculate

% composition
 Empirical formula
 Molecular formula

21
Combustion Analysis

0.1953 g CO2 x 1 mol CO2 x 1 mol C
44.0098 g CO2 1 mol CO2
= 0.004438 mol C x 12.011 g C = 0.05330 g C
1 mol C

0.1000 g H2O x 1 mol H2O x 2 mol H
18.0153 g H2O 1 mol H2O
= 0.01110 mol H x 1.00794 g H = 0.01119 g H
1 mol H
22
Combustion Analysis
0.1000 g of the compound contains
0.05330 g C
0.01119 g H
0.06449 g C + H
 The rest of the compound is oxygen:
0.1000 g compound – 0.06449 g C+H =
0.03551 g O x 1 mol = 0.002219 mol O
15.9994 g

23
Combustion Analysis: % composition

0.1000 g of the compound contains 0.05330 g C,
0.01119 g H, and 0.03551 g O
% C = 0.05330 g C x 100 = 53.30% C
0.1000g
 % H = 0.01119 g H x 100 = 11.19% H
0.1000g
 % O = 0.03551 g O x 100 = 35.51% O
0.1000g
 Total = 100.00% (just checking . . .)

24
Combustion Analysis:
empirical formula

Compound contains 0.004438 mol C, 0.01110 mol
H, and 0.002219 mol O
C.004438H.01110 O.002219
 C(.004438/.002219)H(.01110/.002219)O(.002219/.002219)
 C2.000H5.000O1.000


Empirical formula is C2H5O
25
Combustion Analysis:
molecular formula

The empirical formula is C2H5O. The molar mass
is approximately 90 g/mol



True molar mass =
Empirical molar mass
True molar mass =
Empirical molar mass
90 g/mol
[2(12) + 5(1) + 16]
90 g/mol = 2
45 g/mol
Molecular formula is C4H10O2
26
Oxidation states
The oxidation state (O.S.) or oxidation number is a
convenient but artificial way to describe the
electron environment around an atom
 It is related to the number of electrons gained, lost,
or apparently used in forming compounds
 Oxidation states are assigned using the rules on
page 79 of your text (memorize these in order)

28
Assigning oxidation states
1. The O.S. of each atom in an element is zero.
2. The total of the O.S. of all atoms in any species (formula unit,
molecule or ion) equals the charge on that species.
3. In compounds, Group 1A metals have O.S. +1 and Group 2A metals
have O.S. +2.
4. In compounds, the O.S. of fluorine is –1.
5. In compounds, the O.S. of hydrogen is +1.
6. In compounds, the O.S. of oxygen is –2.
7. In binary compounds with metals, the O.S. of a Group 7A element
is –1, Group 6A element –2, and Group 5A element –3.
29
Assigning oxidation states
Examples 3-7A and 3-7B

What is the oxidation state of the underlined
element in



S8
0
Cr2O72–
+6
Cl2O
+1
KO2
–1/2
What is the oxidation state of the underlined
element in


S2O32–
+2
Hg2Cl2
+1
KMnO4
+7
H2CO
0
30
Nomenclature: Binary Ionic
Compounds
Binary ionic compounds: metal + nonmetal
 Nomenclature of binary ionic compounds

Write name of metal cation (same as element name)
 Write name of nonmetal anion, with element name
modified to end in “–ide”
 No prefixes to indicate number of ions
 Roman numeral shows O.S. of transition metal cation
 Compound is electrically neutral, so in formula
total cation charge = total anion charge

31
Binary ionic compounds
Examples 3-8A and 3-8B

Write the formulas for the compounds
Lithium oxide
 Tin (II) fluoride
 Lithium nitride


Write the formulas for the compounds
Aluminum sulfide
 Magnesium nitride
 Vanadium (III) oxide

32
Binary ionic compounds
Examples 3-8A and 3-8B

Write the formulas for the compounds
Lithium oxide
 Tin (II) fluoride
 Lithium nitride


Li2O
SnF2
Li3N
Write the formulas for the compounds
Aluminum sulfide
 Magnesium nitride
 Vanadium (III) oxide

Al2S3
Mg3N2
V2O3
33
Binary ionic compounds
Examples 3-9A and 3-9B

Write acceptable names for the compounds


CsI
CaF2
FeO
CrCl3
Write acceptable names for the compounds

CaH2
CuCl
Ag2S
Hg2Cl2
34
Binary ionic compounds
Examples 3-9A and 3-9B

Write acceptable names for the compounds

CsI
CaF2
 cesium
iodide
 calcium fluoride

FeO
CrCl3
iron (II) oxide
chromium (III) chloride
Write acceptable names for the compounds

CaH2
 calcium
CuCl
hydride
 copper (I) chloride
Ag2S
Hg2Cl2
silver (I) sulfide
mecury (I) chloride
35
Nomenclature: Binary Molecular
Compounds
Binary molecular compounds: nonmetal+nonmetal
 Nomenclature of binary molecular compounds

Write name of element with positive O.S. first
 Write name of element with negative O.S. second, with
element name modified to end in “–ide”
 Use prefixes to indicate number of atoms of each
element

36
Binary Molecular Compounds
Examples

Write the formulas for the compounds
Carbon tetrabromide
 Dinitrogen pentoxide
 Phosphorus triiodide


Write acceptable names for the compounds

SF6
Cl2O7
IBr3
37
Binary Molecular Compounds
Examples

Write the formulas for the compounds
Carbon tetrabromide
 Dinitrogen pentoxide
 Phosphorus triiodide
CBr4
N2O5
PI3


Write acceptable names for the compounds

SF6
 sulfur
Cl2O7
hexafluoride
 dichlorine heptoxide
 iodine tribromide
IBr3
Watch your
spelling!
38
Nomenclature: Binary acids
Binary acids: certain compounds of H + nonmetal
 Produce hydrogen ions (H1+) when dissolved in
water

Name as acid when focus is on behavior in water
 Write prefix “hydro” for hydrogen
 Write nonmetal element, with name modified to end in
“–ic,” then write acid
 Formula must be electrically neutral

39
Binary acids
Examples

Write the formulas for the compounds
Hydrochloric acid
 Hydroiodic acid
 Hydrosulfuric acid


Write acceptable names for the compounds

HBr
H2S
HF
40
Binary acids
Examples

Write the formulas for the compounds
Hydrochloric acid
 Hydroiodic acid
 Hydrosulfuric acid
HCl
HI
H2S


Write acceptable names for the compounds

HBr
H2S
HF
 hydrobromic
acid
 hydrosulfuric acid
 hydrofuoric acid
41
Nomenclature: Polyatomic Ions
Polyatomic ions are ions consisting of two or more
covalently bound atoms that carry a charge
 Most are anions (exception: ammonium, NH41+)
 Very few polyatomic anion names end in “–ide”

Cyanide, CN1–
Hydroxide, OH1–
 Most names end in “–ate” or “–ite”

42
Nomenclature: Oxoanions

Polyatomic ions that contain oxygen are oxoanions

A nonmetal may form several oxoanions with different
numbers of oxygens
As nonmetal O.S. increases (number of oxygens increases),
name changes sysematically:
ClO1–
ClO21–
ClO31–
ClO41–
hypochlorite
chlorite
chlorate
perchlorate
SO32–
SO42–
sulfite
sulfate

All common oxoanions of halogens are –1
43
Nomenclature: Oxoanions

Polyatomic ions that contain oxygen are oxoanions

Some oxoanions include varying numbers of hydrogens
PO43–
HPO42–
H2PO41–
phosphate
hydrogen phosphate
dihydrogen
phosphate
O.S. of central nonmetal is constant: ion charge changes as
number of hydrogens varies

Prefix “thio–” indicates an S has substituted for an O
SO42–
sulfate
S2O32–
thiosulfate
44
Nomenclature: Oxoacids

Oxoacids are combinations of hydrogen ions (H1+)
and oxoanions
H1+ + oxoanion = acid, a molecular compound
 Metal ion + oxoanion = salt, an ionic compound


Oxoacid name derived from oxoanion name
Change “–ite” to “–ous” and “–ate” to “–ic”
 Add “acid” to end of name


Formulas are electrically neutral
45
Nomenclature: Oxoacids
Examples

Write acceptable names for the compounds


H2SO3
HNO3
HClO
Write the formulas for the compounds
Phosphoric acid
 Nitrous acid
 Perchloric acid

46
Nomenclature: Oxoacids
Examples

Write acceptable names for the compounds
H2SO3
 sulfurous acid


HNO3
nitric acid
HClO
hypochlorous acid
Write the formulas for the compounds
Phosphoric acid
 Nitrous acid
 Perchloric acid

H3PO4
HNO2
HClO4
47
Nomenclature
Examples 3-10A and 3-10B

Name the compounds

SF6

NH4NO3
HNO2
PCl3
Ca(HCO3)2
HBrO
FeSO4
AgClO4
Fe2(SO4)3
48
Nomenclature
Examples 3-10A and 3-10B

Name the compounds

SF6
HNO2
Ca(HCO3)2
 Sulfur
hexafluoride
 Nitrous acid

NH4NO3
PCl3
FeSO4
Calcium hydrogen carbonate
Iron (II) sulfate
HBrO
AgClO4
Fe2(SO4)3
 Ammonium
nitrate
 Phosphorus trichloride
 Hypobromous acid
 Ailver perchlorate
 Iron (III) sulfate
49
Nomenclature
Examples3-11A and 3-11B

Write formulas for the compounds
Boron trifluoride
 Potassium dichromate
 Sulfuric acid
 Calcium chloride
 Aluminum nitrate
 Tetraphosphorous decoxide
 Chromium (III) hydroxide
 Iodic acid

50
Nomenclature
Examples3-11A and 3-11B

Write formulas for the compounds
Boron trifluoride
 Potassium dichromate
 Sulfuric acid
 Calcium chloride
 Aluminum nitrate
 Tetraphosphorous decoxide
 Chromium (III) hydroxide
 Iodic acid

BF3
K2Cr2O7
H2SO4
CaCl2
Al(NO3)3
P4O10
Cr(OH)3
HIO3
51
Slaying the nomenclature dragon
Make flash cards of all the ion names, formulas
and charges and all the acid names and formulas
(Tables 3.1, 3.3, and 3.4 in Chapter 3), and of the
Greek prefixes (mono, di, tri, tetra, penta, hexa,
hepta, octa, nona, deca)
 Concentrate on writing formulas from names
(that’s what’s on the AP exam)
 For ionic formulas and acid, be sure charges
balance!

52
Exercise 32

The hemoglobin content of blood is about 15.5
g/100 mL blood. The molar mass of hemoglobin is
about 64,500 g/mol, and there are 4 Fe atoms in a
hemoglobin molecule. Approximately how many
Fe atoms are present in the 6 L of blood in a
typical adult?
53
Exercise 38

Determine the mass percent of each element in the
antimalarial drug quinine, C20H24N2O2
54
Exercise 45

Determin the empirical formula of
Warfarin, 74.01% C, 5.23% H, and 20.76% O by mass
 Mustard gas, 30.20% C, 5.07% H, 44.58% Cl, and
20.16% S by mass

55
Exercise 47

Indigo has the mass composition 73.27% C,
3.84% H, 10.68% N, and the remainder
oxygen. Its molecular mass is 262.3 amu. What is
the molecular formula of indigo?
56
Exercise 50

The element X forms the chloride XCl4 containing
75.0% Cl, by mass. What is the identity of element
X?
57
Exercise 51

A 0.2612 g sample of a hydrocarbon produces
0.8661 g CO2 and 0.2216 g H2O in combustion
analysis. Its molecular mass is found to be 106
amu. Determine the mass composition, empirical
formula, and molecular formula of this
hydrocarbon.
58
Exercises 57 and 60

Indicate the oxidations state of the underlined
element:


CH4
SF4
Na2O2
C2H3O21–
FeO42–
Nitrogen forms five oxides. Write appropriate
formulas for these compounds if the O.S. of N in
them are +1, +2, +3, +4, and +5, respectively.
59
Exercise 62

Name these compounds
Ba(NO3)2
HNO2
CrO2
KIO3
LiCN
KIO
Fe(OH)2
Ca(H2PO4)2
H3PO4
NaHSO4
Na2Cr2O7
MgC2O4
Na2C2O4
NH4C2H3O2
60
Exercise 64

Assign suitable names to these compounds

ICl
ClF3
SF4
BrF5
N2O4
S4N4
61
Exercise 66

Write correct formulas for










Magnesium perchlorate
Lead (II) acetate
Tin (IV) oxide
Hydroiodic acid
Chlorous acid
Sodium hydrogen sulfite
Calcium dihydrogen phosphate
Aluminum phosphate
Dinitrogen tetroxide
Disulfur dichloride
62
Exercise 77

A sample of MgSO4•xH2O weighing 8.129 g is
heated until all the water of hydration is driven off.
The resulting anhydrous compound, MgSO4,
weighs 3.967 g. What is the formula of the
hydrate?
63
Types of Compounds
QuickTime™ and a
Graphics decompressor
are needed to see this picture.
NaCl, salt
Buckyball, C60
Methane, CH4
64
Molecular Compounds
A molecule is a group of bonded atoms that exists
as a distinct entity
 The atoms in a molecule are held together by
covalent bonds
 Molecular compounds consist of discrete
molecules

70
Water: a molecular compound
71
Acetic acid: a molecular compound
72
SOME MOLECULAR
ELEMENTS
74