Chapter 3
Ionic Compounds
These connections are based on chemistry chemistry- notice the ions
in the picture.. You want to make them long tern memory and sleep
helps. Here is what research says:
•
•
Sleep apparently rearranges
memory within the brain. We
presume that memory is organized
into a more efficient storage
location. That means you can
recollect that information the next
day much better than the day
before.
If you're a college student and you
pull an all-nighter after the piano
lesson, you lose out on the memory
enhancement permanently, even if
you sleep the next night. It's not
practice that makes perfect but it's
practice with a night of sleep that
seems to make perfect. If you don't
snooze, you lose.
Definitions:
A compound results from the combination of two or
more elements in a specific and constant ratio.
A molecule is a combination of a specific number
and kind of elements held together by the force of a
chemical bond which cannot be broken without
creating a different substance.
Salt (sodium chloride);
consist of the elements
sodium and chlorine, in a
specific and constant pattern,
but is considered a
compound, not a molecule.
Distinguishing Compounds and Molecules:
The distinction between compounds and molecules
reflects the nature of the chemical bonding between
the elements. In molecules, the atoms share electrons
in covalent bonds, while in ionic compounds, electrons
are transferred from one atom to another (ionic bonds).
Salt (sodium
chloride); an
example of ionic
bonding.
Methane; CH4 an
example of
covalent bonding.
Ionic Compounds:
Ionic compounds consists of a positively charged ion, a
cation, and a negatively charged ion, an anion, which
occur throughout the compound in a simple and fixed
ratio.
In sodium chloride (NaCl) the sodium ion is positive
(cation) and the chloride ion is negative (anion). In the
compound, they always occur in a ratio of one Na+ to one
Cl-.
The sodium cation.
The chloride anion.
Ionic Compounds:
A requirement for any ionic compound is that all of the
charges must add up to zero. That is, the total charge
on the anions must equal the total charge on the
cations. This is called the Principle of Charge Balance.
Examples:
Mg2+ S2Na+ Br(Na+)2 S2Mg2+ (Br-)2
(+2) and (-2)…the net charge is zero.
(+1) and (-1)…the net charge is zero.
2(+1) and (-2)…the net charge is zero.
(+2) and 2(-1) …the net charge is zero.
Ionic Compounds:
Ionic compounds form very large structures, called
extended structures, in which the ions appear in a
constant ratio. To write a formula for an ionic compound,
we write the simplest whole number ratio of the anions
and cations.
Examples:
Mg2+ S2Na+ Br(Na+)2 S2Mg2+ (Br-)2
is written as…MgS.
is written as…NaBr.
is written as…Na2S.
is written as…MgBr2.
Ionic Compounds:
How do we know what charge will be on various cations
and anions?
¾Metals lose all of their valence electrons to make
a cation that has zero valence electrons.
¾Nonmetals gain valence electrons to make an
anion that has a full octet of electrons.
Examples:
¾Na is a metal with one valence electron. It will lose
this to form Na+.
¾Mg is a metal with two valence electrons. It will lose
these to form Mg2+.
Ionic Compounds:
How do we know what charge will be on various cations
and anions?
¾Metals lose all of their valence electrons to make
a cation that has zero valence electrons.
¾Nonmetals gain valence electrons to make an
anion that has a full octet of electrons.
Examples:
¾Cl is a nonmetal with seven valence electrons. It will
gain one to form Cl-.
¾S is a nonmetal with six valence electrons. It will gain
two to form S2-.
Ionic Compounds:
How do you know what charge will be on various
cations? For simple binary compounds, Group numbers
are associated with common charges.
+1
+2
+3
I
1
2
3
4
5
6
7
+4
VIII
II
Group
III IV V VI VII
Ionic Compounds:
How do you know what charge will be on various
anions? For simple binary compounds, Group numbers
are associated with common charges.
8-Group the # = the negative charge with the anion
-3
-2
-1
I
1
2
3
4
5
6
7
0
VIII
II
Group
III IV V VI VII
In-Class Problem:
Cl prefers -1
I
1
2
VIII
II
III IV V VI VII
Mg prefers +2
3
4
5
6
7
Write a formula for the
compound made of
magnesium and chlorine.
In-Class Problem:
I
1
2
We must have two chlorines
to balance the charge on
each magnesium.
II
III
VIII
IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of
magnesium and chlorine.
MgCl2
In-Class Problem:
O prefers -2
I
1
2
VIII
II
Al prefers +3
III IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of
aluminum and oxygen.
In-Class Problem:
I
1
2
We must find a ratio of Al3+
and O2- which will result in a
net charge of zero.
II
III
VIII
IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of
aluminum and oxygen.
In-Class Problem:
3+
I
1
2
II
Al
O
Al 2O3
2VIII
III IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of
aluminum and oxygen.
In-Class Problem:
Br prefers -1
I
1
2
VIII
II
Ca prefers +2
III IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of calcium
and bromine.
In-Class Problem:
I
1
2
We must find a ratio of Ca2+
and Br- which will result in a
net charge of zero.
II
III
VIII
IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of calcium
and bromine.
In-Class Problem:
2+
I
1
2
II
-
Ca
Br
Ca Br2
VIII
III IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of calcium
and bromine.
In-Class Problem:
O prefers -2
I
1
2
VIII
II
B prefers +3
III IV V VI VII
3
4
5
6
7
Write a formula for the
compound made of boron
and oxygen.
In-Class Problem: (B3+)n(O2-)m
(3 × n) + (-2 × m) = 0
(3n) + (-2m) = 0
3n = 2m
or n/m = 2/3
Therefore, n = 2 and m = 3
Write a formula for the
compound made of boron
and oxygen.
B2O3
Nomenclature of Binary Ionic Compounds:
A binary ionic compound consists of two elements and
the name must include the cation and the anion. The
cation is named first and is simply given the name of
the element. Add the suffix ide to the root of the
anionic element to complete the name; multipliers are
not utilized.
Examples:
MgBr2
Na Cl
K2S
BeBr2
magnesium bromide
sodium chloride
potassium sulfide
beryllium bromide
In-Class Problems:
Provide an acceptable name for the following
binary ionic compounds.
a.
b.
c.
d.
e.
CaBr2
Al2O3
Li2S
CaO
NiCl2
Calcium bromide
Aluminum oxide
Lithium sulfide
Calcium oxide
Nickel chloride
Nomenclature of Polyatomic Ions:
Polyatomic ions consist of charged groups of atoms
bonded together in a fixed ratio and arrangement,
utilizing covalent bonding. Examples which we have
covered include NO3-, ClO3- and the formate anion,
HCO3-. The names and structures of these ions are
important in chemistry and must be mastered.
Common nitrogen containing ions:
NO3NO2NH4+
nitrate
nitrite
ammonium
Nomenclature of Polyatomic Ions:
Common sulfur containing ions:
SO42SO32HSO4HSO3-
sulfate
sulfite
hydrogen sulfate
hydrogen sulfite
Common phosphorus containing ions:
PO43HPO42H2PO4PO33-
phosphate
hydrogen phosphate
dihydrogen phosphate
phosphite
Nomenclature of Polyatomic Ions:
Common carbon containing ions:
CO32HCO3CH3COOCNC2O42-
carbonate
hydrogen carbonate
acetate (C2H3O2-)
cyanide
oxalate
Common chlorine containing ions:
ClO4ClO3ClO2ClO-
perchlorate
chlorate
chlorite
hypochlorite
Nomenclature of Polyatomic Ions:
Common boron containing ions:
BO33-
borate
Common hydrogen containing ions:
H3O+
OH-
hydronium
hydroxide
Other metals:
MnO4CrO42Cr2O72-
permaganate
chromate
dichromate
In-Class Problems:
Name the following compounds.
a.
b.
c.
d.
e.
CaCO3
NH4Cl
Na2SO4
Li2SO3
K2HPO4
Calcium carbonate
Ammonium chloride
Sodium sulfate
Lithium Sulfite
Potassium hydrogen phosphate
In-Class Problems:
Name the following compounds.
a.
b.
c.
d.
e.
Cs2SO4
Mg(CN)2
KNO3
CaCO3
NaHSO3
Cesium sulfate
Magnesium cyanide
Potassium nitrate
Calcium carbonate
Sodium hydrogen sulfite
In-Class Problems:
Write the correct formulas for the compounds
formed from the following ions:
a.
b.
c.
d.
e.
Na+
Ba2+
Al3+
Mg2+
Be2+
and
and
and
and
and
SO42CrO42CO32H2PO4OH-
Na2SO4
BaCrO4
Al2(CO3)3
Mg(H2PO4)2
Be(OH)2
In-Class Problems:
Write the correct formulas for the compounds.
a.
b.
c.
d.
e.
Potassium permaganate
Barium sulfite
Aluminum chlorate
Silver nitrate
Barium cyanide
KMnO4
BaSO3
Al(ClO3)3
AgNO3
Ba(CN)2
Oxidation Numbers
Oxidation number of an element in a compound or a
polyatomic ion shows us how many more or less
electrons it would have than the element in the free state.
There are rules for assigning these oxidation numbers.
It would be useful to know these rules.
I
1
2
3
4
5
6
7
VIII
II
III IV V VI VII
A Sequence of Rules for Assigning
Oxidation Numbers in Ions & Molecules:
¾ The oxidation number of a pure element is zero,
regardless of whether it is molecular or not (i.e. Br2).
¾ Group I metals are always +1. Group II metals are
always +2.
¾ Fluorine is always -1.
¾ In compounds with metals, hydrogen is -1, otherwise it
is always +1.
¾ With a few exceptions, oxygen is always -2.
¾ Halogens are -1, except in compounds with oxygen.
¾ Sulfur and selenium are usually -2, except in
compounds with oxygen.
Oxidation Numbers in Binary Ionic Compounds:
For a simple binary ionic compound, the oxidation
number of each species is the same as the charge on
that species.
Examples:
MgBr2
Li3P
The oxidation number of the magnesium
is +2 and the oxidation number of the
bromine is -1.
The oxidation number of the lithium is +1
and the oxidation number of the phosphorus
is -3.
In-Class Problems:
What is the oxidation number for lead in the
following compounds?
O prefers -2
a. PbO
The oxidation number of the
lead must be +2.
b. PbO2
The oxidation number of the
lead must be +4.
O still prefers -2
How do you think you name these?
In-Class Problems:
What is the oxidation number for iron in the
following compounds?
SO4 is -2
a. FeSO4
The oxidation number of the
iron must be +2.
b. Fe2O3
The oxidation number of the
iron must be +3.
O prefers -2
How do you think you name these?
In-Class Problems:
What is the oxidation number for each element in
SO3?
+6
-2
The oxidation number of the
oxygen will be -2.
SO3
In order for the molecule to be neutral,
the oxidation number of the sulfur must
balance the charges on the oxygens.
The oxidation number on the sulfur must
therefore be given by:
x + 3(-2) = 0 or
x = +6
In-Class Problems:
What is the oxidation number for each element in
nitric acid, HNO3?
The oxidation
number of the
hydrogen will
be +1.
The oxidation number of
the oxygen will be -2.
+1
+5
-2
HNO3
In order for the molecule to be neutral, the oxidation
numbers of the nitrogen and the hydrogen must
balance the charges on the oxygens.
The oxidation number on the nitrogen must
therefore be given by:
(+1) + x + 3(-2) = 0 or
x = +5
HSO3When working with polyatomic ions you
can determine the oxidation number of
the last element by use the oxidation
rules. If there are 3 elements in the
polyatomic ions, you can determine the
oxidation number of the first and last
element by using the oxidation rules.
In-Class Problems:
What is the oxidation number for each element in
hydrogen sulfite ion, HSO3-?
The oxidation
number of the
hydrogen will
be +1.
+1
+4
-2
The oxidation number of
the oxygen will be -2.
HSO3-
In order for the ion to be charged, the oxidation
numbers of the sulfur, hydrogen and oxygen must
add up the charge on the ion.
The oxidation number on the sulfur must
therefore be given by:
(+1) + x + 3(-2) = -1 or
x = +4
In-Class Problems:
Determine the oxidation numbers for each
element in each of the following compounds:
a.
b.
c.
d.
e.
KMnO4
BaSO3
Al(ClO3)3
AgNO3
Ba(CN)2
Carbon brings in 4,
it now has 2;
therefore it is +2.
K,+1 ; Mn, +7;
Ba, +2; S, +4;
Al, +3; Cl, +5;
Ag, +1; N, +5;
Ba, +2; C, +2;
C N
-
O, -2
O, -2
O, -2
O, -2
N, -3
Nitrogen brings in 5,
it now has 8;
therefore it is -3.
In a covalent bond, give the electrons to
element on the right in the periodic table.
Nomenclature of Ionic Compounds Containing
Metals with Variable Oxidation Numbers:
As we have seen, transition metals and some heavier
main group elements (i.e., Sb and Pb) can have more
than one oxidation number. In naming these
compounds, it is necessary to indicate the oxidation
number of these metals. Use Roman numerals.
Examples:
PbO2
PbO
FeCO3
FeBr3
lead (IV) oxide
lead (II) oxide
iron (II) carbonate
iron (III) bromide
In-Class Problems:
Write formulas for each of the following
compounds:
a.
b.
c.
d.
e.
f.
silver nitrate
lead (IV) sulfate
lead (II) hydrogen sulfite
calcium sulfite
iron (II) hydrogen carbonate
aluminum hydrogen phosphate
AgNO3
Pb(SO4)2
Pb(HSO3)2
CaSO3
Fe(HCO3)2
Al2(HPO4)3
In-Class Problems:
1. A cation has a positive charge because:
a)
b)
c)
d)
e)
there are more electrons than protons
it has a positively charged nucleus
there are fewer electrons than protons
there are more protons than neutrons
None of the above are correct.
In-Class Problems:
2. What is the chemical name of Ca(CN)2?
a)
b)
c)
d)
e)
Calcium cyanide
Calcium cyanate
Calcium nitrite
Calcium dicyanide
None of the above are correct.
In-Class Problems:
3. What is the chemical formula for titanium (IV)
nitride?
a)
b)
c)
d)
e)
Ti4N3
Ti4N
TiN4
Ti3N4
None of the above are correct.
In-Class Problems:
4. What is the chemical name of Fe(HSO3)3?
a)
b)
c)
d)
e)
Iron hydrogen sulfite
Iron (III) hydrogen sulfite
Iron (III) tri(hydrogensulfite)
Iron (II) hydrogen sulfite
None of the above are correct.
In-Class Problems:
5. What is the oxidation number of platinum in
Pt2F11–?
a)
b)
c)
d)
e)
10
12
6
5
8
2(+5) + 11(-1) = -1
Pt2F11–
In-Class Problems:
6. The oxidation number of sulfur in S8 is:
a)
b)
c)
d)
e)
+8
+4
-2
0
None of the above are correct.
In-Class Problems:
7. The oxidation numbers of the metals in the three
compounds shown below are (in the order
shown):
+2
Ni(NO3)2
a)
b)
c)
d)
e)
+2
FeSO4
+3
Rh2(CO3)3
+2, +3, +6
+2, +2, +6
+2, +2, +2
+3, +3, +3
None of the above are correct.
In-class Questions
Determine the oxidation numbers for each element in
each of the following compounds
Ag2HPO4
Cu(NO2)2
AgNO3
Fe(HCO3)3
Al2(HPO4)3
Cu(NO2)2
Al(C2H3O2)3
Al2(Cr2O7)3