Transcript Chapter 5 Lecture

Chapter 5
Molecules and Compounds
Sucrose molecule (sugar), contains C, H, and O atoms.
However, the properties of sucrose are very different
from those of C, H, and O alone. The properties of a
compound are, in general, different from the properties
of the elements that compose it.
molecular formula C12H22O11
2006, Prentice Hall
CHAPTER OUTLINE
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Law of Constant Composition
Octet Rule and Ions
Ionic Charges
Definitions of Molecules and Compounds
Types of Compounds
Binary Ionic Compounds (Type I and Type II)
Polyatomic Ions
Binary Molecular Compounds
Naming Acids and Oxyacids
Formula Mass
2
LAW OF DEFINITE
COMPOSITION
Mass
of thethe
 In
Based
a pure
oncompound,
this
law,
mass
elements
of an element
are
Mass of N Mass of H
sample
always
can
be determined
present
in the
from
same
its mass
definite
percent
proportion
in
a compound.
by
mass.
Sample
1
1.840
g
1.513 g
0.327 g
Sample 2
2.000 g
1.644 g
0.356 g
1
.
5
1
3
g
x
1
0
0
=
8
2
.
2
3
%
% N in Sample 1 =
1
.
8
4
0
g
1
.
6
4
4
g
x
1
0
0
=
8
2
.
2
0
%
% N in Sample 2 =
2
.
0
0
0
g
3
Example 1:
Barium iodide, BaI2, contains 35.1% barium by
mass. How many grams of barium does an 8.50
g sample of barium iodide contain?
35.1
g
B
a
2.98 g
8
.
5
0
g
B
a
I
x
=
B
a
2
100 g
B
a
I
2
3 significant figures
4
Example 2:
When 12.66 g of calcium are heated in air,
17.73 g of calcium oxide is formed. What is
the percent of oxygen in this compound?
Mass of oxygen = 17.73 g – 12.66 g = 5.07 g
5
.
0
7
g
x
1
0
0
=
2
8
.
6
%
Percent oxygen =
1
7
.
7
3
g
3 significant figures
5
OCTET RULE
& IONS
 Most elements, except noble gases, combine to form
compounds. Compounds are the result of the
formation of chemical bonds between two or more
different elements.
 In the formation of a chemical bond, atoms lose,
gain or share valence electrons to complete their
outer shell and attain a noble gas configuration.
 This tendency of atoms to have eight electrons in
their outer shell is known as the octet rule.
6
FORMATION
OF IONS
 An ion (charged particle) can be produced when
an atom gains or loses one or more electrons.
Metals form
cations
A cation (+ ion) is formed when a
neutral atom loses an electron
7
5.1
FORMATION
OF IONS
 An anion (- ion) is formed when a neutral
atom gains an electron.
Non-metals
form anions
8
5.1
IONIC CHARGES
 The
For most
ionic main
charge
group
of anelements,
ion is dependent
the ionicon
charges
the can
number
be
determined
of electrons
from their
lost orgroup
gained
number,
to attain
as ashown
noble
gas configuration.
below:
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Definition of Molecule and Compound
• molecule - consist of at least two different atoms in a definite
arrangement held together by very strong chemical bonds.
• compound is a substance consisting of two or more elements in
fixed and definite proportions
Formulas Describe Compounds
• a compound is a distinct substance that is
composed of atoms of two or more elements
• a compound can be described by the number
and type of each atom in the simplest unit of the
compound
– molecules or ions
• each element is represented by its letter symbol
• the number of atoms of each element is written
to the right of the element as a subscript
Formulas Describe Compounds
water = H2O \ two atoms of
hydrogen and 1 atom of oxygen
table sugar = C12H22O11 \ 12
atoms of C, 22 atoms of H and 11
atoms O
Order of Elements in a Formula
• metals written first
– NaCl
• nonmetals written in order
from Table 5.1
– CO2
– there are occasional
exceptions for historical or
informational reasons
• H2O fits rule, but does NaOH?
Table 5.1
Order of Listing
C P N H S
Nonmetals
in Chemical Formulas Tro's Introductory Chemistry,
Chapter 5
I Br Cl O F
13
Types of Chemical Formulas
• An empirical formula gives the relative number of
atoms of each element in a compound.
• A molecular formula gives the actual number of
atoms of each element in a molecule of the
compound.
• For example, the molecular formula for hydrogen
peroxide is H2O2, and its empirical formula is HO.
• The molecular formula is always a whole number
multiple of the empirical formula.
• For many compounds, such as H2O, the molecular
formula is the same as the empirical formula.
• A structural formula uses lines to represent chemical
bonds and shows how the atoms in a molecule are
connected to each other.
Comparison of Formulas and Models for
Methane, CH4
• The molecular formula of methane indicates that methane
has 1 carbon atom and 4 hydrogen atoms.
• The structural formula shows how the atoms are connected:
each hydrogen atom is bonded to the central carbon atom.
• The ball-and-stick model and the space-filling model
illustrate the geometry of the molecule: how the atoms are
arranged in three dimensions.
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
Tro's Introductory Chemistry,
anions
Chapter 5
Molecular Elements
• Certain elements occur as 2 atom molecules
• Rule of 7’s
–
–
–
–
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
O2
F2
Cl2
Br2
I2
17
Molecular Compounds
• two or more
nonmetals
• smallest unit is a
molecule
Ionic Compounds
• metals + nonmetals
• no individual
molecule, instead
these have 3dimensional array of
cations and anions
made of formula
units (NaCl)
IONIC
COMPOUNDS


 After
Ionic
Ionic bonds
bonding,
compounds
occur
each
contain
between
atom ionic
achieves
metals
bonds,
and
a complete
which
non-metals.
occur
shell
(noble
when electrons
gas configuration).
are transferred between two atoms.
Metal
Nonmetal
20
IONIC
COMPOUNDS
 Atoms

The smallest
that gain
lose
particles
electrons
electrons
of ionic
(metals)
(non-metals)
compounds
form form
positive
are
negative
ions
(cations).
(not
ions
atoms).
(anions).
Anion
Cation
21
IONIC CHARGES
AND FORMULAS
 The
For example,
formula
sum
of the
of
the
ionic
an+1ionic
charge
charges
compound
oninthe
thesodium
indicates
formulaion
isthe
is
always
number
zero,
cancelled
which
and
byindicates
kinds
the –1of
charge
that
ions the
that
on total
the
make
chloride
number
up theion,
of
ionic
positive
to form
compound.
acharges
net zero
is charge.
equal to the total number of negative
charges.
loses 1 e
gains 1 e
(1+) + (1) = 0
22
IONIC CHARGES
AND FORMULAS
 When
For example,
chargessince
between
eachthe
magnesium
two ions do
loses
not2balance,
electrons,
subscripts
and each chloride
are usedgains
to balance
one electron,
the charges.
2 chlorides are
needed to balance the charge of the magnesium ion.
 Therefore magnesium chloride is written as MgCl2.
MgCl2
loses 2 e
Each
gains 1 e
(2+) + 2(1) = 0
23
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
= atomic element
= ionic compound
= molecular element
= molecular compound
= molecular compound
= atomic element
TYPES OF
COMPOUNDS

 Compounds
Compounds can
are be
pure
classified
substances
as one
that
ofcontain
two types:
2 or more elements combined in a definite
Two nonproportion by mass.
metals
Metals and
non-metals
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Nomenclature of Compounds
Common Names – Are Exceptions
(like nicknames)
H2O = water, steam, ice
NH3 = ammonia
CH4 = methane
NaCl = table salt
C12H22O11 = table sugar
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 one possible charge
– determine charge by charge on
anion
How do you know a
metal cation is Type II?
its not Type I !!!
BINARY IONIC
COMPOUNDS (TYPE I)
 Binary compounds contain only two elements.
 Ionic compounds are formed by combination of a
metal and a non-metal.
 Type I ions are those cations that form only one
ion.
 In these compounds, charges of the cations must
equal the charges of the anions since the net
charge is zero.
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BINARY IONIC
COMPOUNDS (TYPE I)
 Subscripts are used to balance the charges
between cations and anions.
sodium bromide
Na+
No
subscripts
needed
Br
potassium sulfide
K
K2++
S2
+1 -1 = 0
+2
+1 -2
-2 =
 00
NaBr
K2S
29
Example 1:
Write formulas for the following ionic compounds:
calcium chloride
Ca2+
Cl
Cl2
sodium sulfide
Na
Na2++
S2
+2
+2 -2
-1 =
 00
+2 -2
-2 = 00
+1
CaCl2
Na2S
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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
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BINARY IONIC
COMPOUNDS (TYPE I)
MgCl2
NaI
AlF3
magnesium chloride
sodium iodide
aluminum fluoride
32
Example 2:
Name the following ionic compounds:
Na3P
sodium phosphide
BaCl2
barium chloride
33
BINARY IONIC
COMPOUNDS (TYPE II)
 Type II ions are those cations that form more than
one ion.
 When naming compounds formed from these
ions, include the ionic charge as Roman numeral,
in parentheses, after the metal’s name.
 This method of nomenclature is called the “stock”
system.
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NAMING AND WRITING
IONIC FORMULAS
 Some
Differentiating
When
elements
writing ionic
produce
between
formula,
only
type one
Iknowing
and
ion
II(Type
ions
the is
charge
I) while
of
the ionsproduce
others
important,
aresince
important
two
theor
naming
more
since ions
the
system
net
(Type
charge
is different
II). on the
for
compound
each.
Shown
must
below
be zero.
are the common ions of each type:
Type I
Type II
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BINARY IONIC
COMPOUNDS (TYPE II)
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 (only difference from type II!)
– determine charge from anion charge
3. nonmetal anion named by changing the ending
on the nonmetal name to -ide
36
BINARY IONIC
COMPOUNDS (TYPE II)
+2
? -1
-1
FeCl2
iron (II) chloride
? -2 = 0
+3
? -1
-1
FeCl3
iron (III) chloride
? -3 = 0
37
BINARY IONIC
COMPOUNDS (TYPE II)
+1
? -2
-2
Cu2O
2? -2 = 0
+2? -2
-2
CuO
copper (I) oxide
Roman numeral
DOES NOT
represent the
subscript
copper
(II) oxide
? -2 = 0
38
BINARY IONIC
COMPOUNDS (TYPE II)
 Type II cations can also be named by an older
method (classical).
 In this system, cations with the higher charge
end in –ic, while cations with the lower charge
end in –ous.
 In this system, some cations are named based on
their Latin roots.
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CLASSICAL SYSTEM
(DERIVED FROM LATIN)
gold (aurum for Aurora the Roman goddess of the dawn)
silver (argentum for 'bright')
copper (cuprum for 'Cyprus' where the Romans first obtained copper)
tin (stannum for alloys containing lead)
lead (plumbum for 'lead')
mercury (hydrargyrum for 'liquid silver' or quick silver)
antimony (stibium for 'not alone')
iron (ferrum for 'firmness‘)
potassium (kalium via the Arabic qali for alkali)
sodium (natrium for soda)
40
BINARY IONIC
COMPOUNDS (TYPE II)
+2 -1
FeCl2
ferrous chloride
Higher
charge
+3 -1
FeCl3
Lower
charge
ferric chloride
41
BINARY IONIC
COMPOUNDS (TYPE II)
+1 -2
Cu2O
cuprous oxide
Higher
charge
+2 -2
CuO
Lower
charge
cupric oxide
42
Example 1:
Name each of the following compounds using the
stock and classical nomenclature system:
Stock
+2
? -1
-1
SnCl2
tin (II) chloride
Classical
? -2 = 0
Lower
charge
stannous chloride
43
Example 1:
Name each of the following compounds using the
stock and classical nomenclature system:
Stock
+1
? -2
-2
Cu2S
2? -2 = 0
copper (I) sulfide
Lower
charge
cuprous sulfide
Classical
44
Example 2:
Write formulas for each of the following compounds:
+2
Tin (II) bromide
-1
Sn Br
Br2
+2 -2
-1 =
0
SnBr2
45
Example 2:
Write formulas for each of the following compounds:
+4 -2
Stannic oxide
Sn
O
O2
+4 --24=00
SnO2
46
Examples
What, if anything, should go into the parenthesis
•
•
•
•
•
LiCl = lithium (X) chloride
AlCl3 = aluminum (X) chloride
PbO = lead (II) oxide
PbO2 = lead (IV) oxide
Mn2O3 = manganese (III ) oxide
POLYATOMIC IONS
 Some ionic compounds contain polyatomic ions,
an ion composed of several atoms bound together.
48
Patterns for Polyatomic Ions
1. elements in the same column form
similar polyatomic ions
– same number of O’s and same charge
ClO3- = chlorate \ BrO3- = bromate
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
Periodic Pattern of Polyatomic Ions
-ate groups
IIIA
-3
BO3
IVA
VA
VIA
VIIA
-2
CO3
-1
NO3
-2
SiO3
-3
PO4
-2
SO4
-1
ClO3
-3
AsO4
-2
SeO4
-1
BrO3
-2
TeO 4
-1
IO3
Patterns for Polyatomic Ions
• -ate ion
– chlorate = ClO3-1
• -ate ion + 1 O  same charge, perprefix
– perchlorate = ClO4-1
• -ate ion – 1 O  same charge, -ite
suffix
– chlorite = ClO2-1
• -ate ion – 2 O  same charge, hypoprefix, -ite suffix
– hypochlorite = ClO-1
Naming Ionic Compounds Containing a
Polyatomic Ion
• Some examples of more than two ions in
the series.
ClO −
ClO2−
ClO3−
ClO4−
hypochlorite
chlorite
chlorate
perchlorate
BrO −
BrO2−
BrO3−
BrO4−
hypobromite
bromite
bromate
perbromate
IO −
IO2−
IO3−
IO4−
hypoiodite
iodite
iodate
periodate
When naming these ions in the homework, be sure to
include the word ion in your answer, as in “perchlorate
ion.”
© 2012 Pearson Education, Inc.
POLYATOMIC
COMPOUNDS
 When writing formulas for polyatomic compounds,
treat the polyatomic ion as one group.
potassium nitrate
K+
NO3–
calcium hydroxide
Ca2+
(OH
OH– )2
+1 -1 = 0
+2
+2 -2
-1 =
 00
KNO3
Ca(OH)2
53
POLYATOMIC
COMPOUNDS
ammonium acetate
NH4+
C2H3O2–
+1 -1 = 0
NH4C2H3O2
sodium sulfate
Na
Na2++
SO42–
+2
+1 -2
-2 =
 00
Na2SO4
54
POLYATOMIC
COMPOUNDS
copper (II) nitrate
Cu2+
(NO
NO33––)2
+2
+2 -2
-1 =
 00
Type II
Roman numeral
represents charge
of ion
Cu(NO3)2
Alternate name =cupric nitrate
55
Example 2:
Name the following polyatomic compounds:
Mg(OH)2
NaCN
magnesium hydroxide
Type II ion
(Requires roman
sodium
Type
I ioncyanide
numeral)
(Does not require
roman numeral)
Fe2(SO4)3
iron (III) sulfate
+3 2
ferric sulfate
56
Subclasses
• Compounds containing a metal and a
nonmetal = binary ionic
– Type I and II
• Compounds containing a polyatomic ion =
ionic with polyatomic ion
BINARY MOLECULAR
COMPOUNDS
 Molecular compounds are formed by
combination of 2 or more non-metals.
 The smallest particles of molecular compounds
are molecules.
 These compounds are named similar to ionic
compounds, with the second element named
based on its root and suffix “-ide”.
58
BINARY MOLECULAR
COMPOUNDS
 Greek prefixes are used to indicate the number
of atoms in these compounds.
Number
Prefix
Number
Prefix
1
mono-
6
hexa-
2
di-
7
hepta-
3
tri-
8
octa-
4
tetra-
9
nona-
5
penta-
10
deca59
Examples:
Name the following binary molecular compounds:
carbon disulfide
CS2
First atom uses a
indicates 1
prefix only when
carbon atom
more than one
atom is present
Second atom
indicatesalways
2
uses a
sulfur atoms
prefix
60
Examples:
Name the following binary molecular compounds:
iodine heptafluoride
IF7
indicates 1
iodine atom
indicates 7
fluorine atoms
61
SUMMARY OF BINARY
NOMENCLATURE
Ionic
Molecular
Type I
Type II
62
Naming Acids
• Contain H+ cation and
anion
– in aqueous solution
• Binary acids have H+
cation and nonmetal anion
• Oxyacids have H+ cation
and polyatomic anion
Naming Acids
• Binary Acids = hydro prefix + stem of the name
of the nonmetal + ic suffix
Example: HCl  hydrochloric acid
• Oxyacids
– if polyatomic ion ends in –ate = name of polyatomic
base name of oxyanion + -ic
acid
ion with –ic suffix
Example: HNO3  nitric acid
– if polyatomic ion ends in –ite = name of polyatomic
ion with –ous suffix
acid
base name of oxyanion + -ous
Example: H2SO3  sulfurous acid
ACIDS
 Acids are molecular compounds that form ions
when dissolved in water.
Binary Acids
 Formulas are written similar to binary ionic
compounds, assigning a +1 charge to hydrogen.
+1 -1
+1 -2
HCl
H2S
65
NAMING
BINARY ACIDS
 When naming the acids, use hydro- prefix,
followed by the name of the non-metal with an
–ic ending, followed with the word acid.
HCl
hydrochloric acid
H2S
hydrosulfuric acid
HF
hydrofluoric acid
66
POLYATOMIC
ACIDS
 Several polyatomic acids are important in the
study of chemistry, and their names must be
learned.
 These acids and the polyatomic ions that form
from their ionization are as follows:
 Most of these are oxyacids
67
POLYATOMIC
ACIDS
nitric acid
sulfuric acid
phosphoric acid
HNO3
NO3
nitrate
H2SO4
SO42
sulfate
H3PO4
PO43
phosphate
68
POLYATOMIC
ACIDS
carbonic acid
H2CO3
CO32
carbonate
HCO3
bicarbonate
acetic acid
HC2H3O2
C2H3O2
acetate
69
The names of acids containing oxyanions ending with -ite take this
form:
base name of oxyanion + ous
The names of acids containing oxyanions ending with -ate take
this form:
base name of oxyanion + ic
Names of Some Common Oxyacids and
Their Oxyanions
Formula Mass:
The Mass of a Molecule or Formula Unit
• also known as molecular mass
• For any compound, the formula mass is the sum of the
atomic masses of all the atoms in its chemical formula:
Mass of 1 molecule of H2O
= 2(1.01 amu H) + 16.00 amu O = 18.02 amu
THE END
73