Key
Question:
Why Do Atoms Combine In Certain Ratios?
Review of Oxidation
Numbers
Review of Oxidation Numbers
 All
compounds have an electrical charge of zero
(they are neutral).
 An oxidation number indicates the charge on the
atom (or ion) when electrons are lost, gained, or
shared in chemical bonds.
Oxidation Numbers
A
sodium atom always ionizes
to become Na+ (a charge of
+1) when it combines with
other atoms to make a
compound.
 Therefore, we say that sodium
has an oxidation number of 1+.
What is chlorine’s oxidation number?
Ionic Bonds
 On
the periodic table, strong electron donors are on the
left side (alkali metals).
 Strong electron acceptors are on the right side
(halogens).
 The further apart two elements are on the periodic table,
the more likely they are to form an ionic compound.
Covalent Bonds
 Covalent
compounds form when elements have roughly
equal tendencies to accept electrons.
 Elements that are both nonmetals and therefore close
together on the periodic table tend to form covalent
compounds.
Oxidation Numbers, Lewis Structures And
Chemical Formulas
 Remember,
the oxidation numbers for all the atoms in a
compound must add up to zero.
Multiple Oxidation Numbers
 Some
periodic tables list
multiple oxidation numbers
for most elements.
 This is because more
complex bonding is possible.
Naming Compounds and
Writing Formulas
5 Types Of Chemical Compounds
•Binary ionic
- metal ion – nonmetal ion
•Ternary ionic
- at least one ion is a
polyatomic ion
•Binary molecular
- two nonmetals
•Binary acid
- H – nonmetal
•Ternary acid
- H – Polyatomic ion
Tips To Keep In Mind When Naming And
Writing Formulas:
•Always keep your Periodic Table handy – You should
have it in front of you ALWAYS when you are naming and
writing formulas.
•Remember that metals (except Hydrogen) are found to the
left of the stairstep on the Periodic Table.
•Nonmetals are found on the right side of the stairstep of
the Periodic Table.
•Metalloids are the 7 elements on or below the stairstep
except Al and At. For naming purposes they will tend to
behave like nonmetals.
Naming Binary Compounds
A
binary ionic compound is held together by ionic
bonds.
 Binary molecular compounds consist of covalently
bonded atoms.
 Each type of compound has its own naming rules.
How Do You Name Binary Ionic Compounds?
(Composed Of Two Elements – A Metal And A
Nonmetal)
•Name the first ion
•From groups 1, 2, 3, 13, zinc, cadmium, or silver.
(You must use a Roman Numeral with the name for
the other metals – we’ll discuss this later.)
•Name the second ion changing the suffix to –ide.
Naming Binary Ionic Compounds
 MgBr2 is
magnesium (name
of first element) + brom (root
name of second element) +
ide suffix = magnesium
bromide
Examples
This is two metals – not a binary ionic
BaNa2 You
Theshould
name recognize
of this is Banana
a problem
(haha!!)
with this
compound
one
What is the name of this
compound:
HIJKLMNO?
WATER – “H” to “O”
You have to admit – that was
funny!
Exit Quiz
NaCl
Sodium Chloride
Name the metal ion
CaO
Calcium Oxide
Al2S3
Aluminum Sulfide
MgI2
Magnesium Iodide
Name the nonmetal ion, changing
the suffix to –ide.
What About The Transition Metals And Using Roman
Numerals? How Does That Work?
Let’s See.
FeO
Iron (II) Oxide
Notice – metal and nonmetal.
Name the first ion. Since the first ion is a transition
element, you must use a Roman Numeral to
represent the charge.
How do you know the charge?
Deductive reasoning.
•All compounds are neutral.
•Oxygen has a -2 charge (group 16)
Isn’t this easy
and FUN!!!
•Therefore, iron must have a +2 charge since there
is one iron and one oxygen. Iron gets a Roman
Numeral (II).
Cu2S
Name the first ion. Since it is a transition metal, you
must use a Roman Numeral.
Which Roman Numeral? The Roman Numeral is the
same as the charge of the ion.
How do you find the charge?
Deductive reasoning!
•All compounds are neutral
•Sulfur has a -2 charge (group 16)
Copper (I)
Sulfide
•There are two coppers.
•Therefore each copper must have a +1 charge for all
ions to be neutral
MnO2
Name the first ion. Since it is a transition metal,
you must use a Roman Numeral.
How do you determine the Roman Numeral?
Manganese (IV)
oxide
It is the same as the charge.
What is the charge of Mn?
•All compounds are neutral.
•Oxygen (group 16) has a -2 charge.
•There are two oxygens and one Mn.
•Therefore Mn must have a +4 charge for this
compound to be neutral.
So Why Must We Use Roman Numerals With
Transition Elements?
•The metals in groups 1, 2, 3, and 13 have single, definite charges.
•Group 1 metals have a +1 charge.
•Group 2 metals have a +2 charge.
•Groups 3 and 13 metals have a +3 charge.
•Transition metals may have multiple charges – usually two different
positive charges.
For example, there are two copper oxide compounds:
Cu2O and CuO
Copper II
I oxide
oxide
Copper is +2
+1
We can’t just say Copper oxide. Which one of
these is Copper oxide? We must distinguish these
by using a Roman Numeral
There Are Three Transition Elements Which Do Not
Require A Roman Numeral Because They Have Single
Definite Charges. These Are
Zinc – Zn2+
Cadmium – Cd2+
Silver – Ag+
You need to remember the charges for these.
Ag2O
Silver oxide
ZnCl2
Zinc chloride
Name the first ion.
Name the second ion changing the
suffix to –ide.
No Roman
Numerals needed
for these.
Name the first ion.
Name the second ion changing the
suffix to –ide.
How Do You Write Formulas For Binary Ionic Compounds
Given The Name?
Two Simple Steps:
1. Write the symbol and charge of each ion
2. Balance the charges by providing subscripts
Magnesium chloride
Mg2+
MgCl2
ClCl-
Write the symbol and charge of each ion.
Balance the charges by supplying subscripts.
Subscripts tell how many of each atom is
present.
You need a second Cl-1 to balance the charges
Iron (III) bromide
Fe3+
FeBr3
Br Br Br -
Write the symbol and charge of each ion.
The charge of the iron is provided by the
Roman Numeral.
Balance the charges by supplying
subscripts. The subscripts tell how many
of each ion is needed to balance the
compound.
You’ll need three bromine ions to balance
the one iron.
Aluminum Sulfide
Al3+
Al3+
Al2S3
S2S2S2-
Write the symbol and charge of each ion.
Balance the charges by supplying subscripts.
In this case the charges do not evenly divide
into each other. You must find the least
common multiple. SIX
How many aluminums are needed to arrive at
a +6 charge?
2
How many sulfurs are needed to arrive at a -6
charge?
3
Writing Formulas a Little Quicker
Iron and oxygen combine to form a compound. Iron (Fe)
has an oxidation number of 3+. Oxygen (O) has an
oxidation number of 2–.
Predict the chemical formula of this compound.
Writing Formulas a Little Quicker
Given
1.

… Fe3+ and O2–

Write the subscripts so that the sum of the
oxidation numbers equals zero.
Solution
2.

Two iron atoms = 2 × (3+) = 6+

Three oxygen atoms = 3 × (2–) = 6–
Writing Formulas a Little Quicker
2-
3+
Fe
3
O
x
2
=
6
Writing Formulas a Little Quicker
Fe 3+
O
2+
+
Fe 3+
=
+6
O
2-
+
+6
-6
0
O
=
2-6
Writing Formulas a Little Quicker
3+
2-
Fe 2 O 3
Exit Quiz – Formula for magnesium chloride?
2+
MgCl2
1-
Exit Quiz – Formula for sodium oxide?
1+
Na2O
2-
Exit Quiz – Name for:
3+ 2-
Fe2O3
Iron (III) oxide
Exit Quiz – Formula for:
4+ 2-
CrO2
Chromium (IV) oxide
Exit Quiz – Charge on Chromium?
6+ 2-
Cr2O72-
Second Category Of Compounds – Ternary Ionic
Compounds.
These Compounds Contain At Least One
Polyatomic Ion.
What is a polyatomic ion?
Let’s look at the name to try to understand.
•It is an ion – that means it has a charge.
•It is polyatomic – that means it is made of more than one
atom.
Let’s look at some examples of polyatomic ions.
CO32- carbonate
This ion is composed of one carbon
and three oxygens and the entire group
has a charge of -2.
Polyatomic ion – Group of atoms that act as a unit and
carry a charge.
You have been given a list of other polyatomic ions
You need to learn these!!!
How Do You Recognize Ternary Ionic Compounds?
Composed of two ions in which at least one is a polyatomic ion.
There is only one positive polyatomic ion (NH4+)
Three possible types of Ternary Ionic Compounds:
Polyatomic Ion
•Ammonium
+ negative ion (nonmetal)
•Metal (positive ion)
+ negative polyatomic ion
•Ammonium
+ negative polyatomic ion
Naming Compounds with Polyatomic ions
 NH4Cl
is ammonium (the
name of the ion from chart) +
chlor (root name of the
second element) + ide suffix
= ammonium chloride.
How Do You Name Ternary Ionic Compounds?
1. Name the first ion.
2. Name the second ion. Isn’t that simple??!!
Examples:
Na2CO3
When you look at this compound you should
recognize that this is NOT binary. There are
THREE elements present. When you see this,
Sodium carbonate immediately look for a polyatomic ion.
Carbonate is present here.
Notice that you do NOT
change the suffix – just
name the polyatomic
Name the first ion.
ion
Name the second ion.
Fe(OH)3
Iron (III) hydroxide
Since there are 3
OH groups, each
with a -1 charge,
the charge of the
iron must be +3 for
the compound to
be neutral
Name the first ion.
Remember that iron requires a Roman Numeral
since it is a transition element. What Roman
Numeral should be used?
The Roman Numeral comes from the charge of
the ion. How do you find the charge of the iron?
You know two things:
•All compounds are neutral.
•You know the charge of OH (-1)
Name the polyatomic ion.
NH4Cl
Name the first ion.
Ammonium
chloride
Name the second ion.
Notice that since the second ion is a nonmetal that, like binary ionic
compounds, the suffix of the nonmetal changes to –ide.
Name the first ion.
(NH4)3PO4
Ammonium
phosphate
Name the second ion.
Looks like a monster, but it’s really a pussycat.
Cu2SO4
Copper (I) sulfate
Name the first ion.
You should realize that you need a
Roman Numeral since copper is a
transition metal.
The Roman Numeral is the same as
the charge.
What is the charge?
The charge of sulfate is -2.
Since there are two coppers, the
charge of the copper must be +1.
Name the second ion.
How Do You Write Formulas For Ternary Ionic
Compounds?
Very Much Like Writing Formulas For Binary Ionic
Compounds.
Three Steps:
1. Write the formulas/symbols of each ion.
2. Balance the charges by supplying subscripts.
3. If a subscript is needed for a polyatomic ion, it must be put in
parentheses with the subscript on the outside.
Let’s do some!!
Aluminum nitrate
Al3+
NO3-
Al(NO3)3
First, you can tell from the name that there
is a polyatomic ion present (nitrate). All
binary ionic compounds have suffixes of –
ide.
Write the formula/symbol and charge of each ion.
Balance the charges by supplying subscripts.
Since Al is +3 and NO3 is -1, you need a total of 3NO3- to
balance one Al3+
Since you will need a subscript of 3 for NO3-, you need to put
this in parentheses with the 3 outside.
Lead (IV) acetate
Pb4+
C2H3O2-
Pb(C2H3O2)4
Calcium phosphate
Ca2+
PO43-
Ca3(PO4)2
Write the formula/symbol and charge of
each ion.
Balance the charges by supplying
subscripts. Since Pb is +4 and C2H3O2 is 1, you will need 4 C2H3O2-1 to balance
1Pb+4
Write the formula/symbol and charge of
each ion.
Balance the charges by supplying
subscripts. Since Ca is +2 and PO4 is -3,
you will need 3 Ca+2 to balance 2 PO4-3
Exit Quiz
 Al3+
combines with sulfate (SO4)2– to make aluminum
sulfate.
 Write the chemical formula for aluminum sulfate.
Exit Quiz Answer
3+
2-
Al 2 (SO4) 3
The Third Category of Compounds –
Binary Molecular
What are Binary Molecular Compounds?
These compounds contain two elements (binary).
•The term “molecular” indicates that these elements are
joined by a covalent bond.
•They must therefore be nonmetals.
•Bottom line – 2 elements – both nonmetals
•To name and write formulas for these, you must know
some numerical prefixes.
Naming – You Must Use Prefixes.
1 = mono
3 = tri
5 = penta
7 = hepta
9 = nona
2 = di
4 = tetra
6 = hexa
8 = octa
10 = deca
Steps
1. The first nonmetal only gets a numeric prefix when there is more
than one. No prefix if there is only one.
2. The second element always gets a numeric prefix and always has a
suffix of -ide
Naming Binary Molecular Compounds
 As
with binary ionic compounds, the ending of the name of
the second element in the compound is modified by adding
the suffix –ide.
CO2
Carbon dioxide
CO
Carbon monoxide
Name the first element. Since there is
only one, no prefix is needed.
The second element always gets a prefix
and a suffix of –ide.
N2O4
Dinitrogen tetraoxide
H2O
Dihydrogen monoxide
CCl4
Carbon tetrachloride
Name the first element. Since
there are two present, the prefix
“di” is needed. The second
element always gets a prefix and
a suffix of –ide.
AlCl3
What do you think about this one???
Be careful. This is a metal and nonmetal.
Always keep your Periodic Table in front of
you for reference.
You may have been tempted to say
“aluminum trichloride”. This is
INCORRECT!
This is a binary IONIC compound. No
prefixes are used. Simply name it
aluminum chloride.
Given The Names Of Binary Molecular Compounds,
How Do You Write The Formulas?
Very easily done!!! The prefixes tell you how to write the
formulas. DO NOT CONSIDER CHARGES. NONMETALS
ARE ALL NEGATIVE SO TO USE CHARGES DOES NOT
WORK!
Silicon dioxide
Silicon and oxygen are both nonmetals.
SiO2
The lack of a prefix on silicon means
that there is only ONE silicon.
The prefix “di” in front of oxide means
that there are TWO oxygens.
Diphosphorous pentachloride
P2Cl5
Phosphorous and chloride are both
nonmetals.
The prefix “di” means that there are TWO
phosphorouses (Is that a word?)
The prefix “penta” before chlorine means
that there are five chlorines.
Nitrogen monoxide
NO
Nitrogen and oxygen are both
nonmetals.
The lack of a prefix on nitrogen
means only ONE nitrogen.
The prefix “mono” on oxygen
indicates ONE oxygen.
Is this not sooooooo easy!??
Exit Quiz
CO2
SO3
Carbon dioxide
Sulfur trioxide
SO
CO
Sulfur monoxide
Carbon monoxide
N2O5
B2O3
Dinitrogen pentaoxide
Diboron trioxide
CF4
NF5
Carbon tetrafluoride
Nitrogen pentafluoride
More Practice with Covalent Compounds
Covalent compounds are made of
two nonmetals, which from the
periodic table are always expected
to be negative
More Practice with Covalent Compounds
But since covalent compounds are
neutral species, it is not possible
for every element to retain its
negative oxidation number
More Practice with Covalent Compounds
ONLY THE MORE ELECTRONEGATIVE
ELEMENT keeps its negative oxidation
number. Other nonmetals must adapt to
keep the compound neutral
Electronegativity Trend
More Practice with Covalent Compounds
-2
SO2
Since oxygen is the more
electronegative element, it will
have its normal oxidation
number.
More Practice with Covalent Compounds
+4 -2
SO2
The compound is neutral, so the
oxidation number of sulfur will be
sufficient to balance out the two
oxygen atoms. What is it?
More Practice with Covalent Compounds
-1
OF2
Since fluorine is the more
electronegative element, it will
have its normal oxidation
number.
More Practice with Covalent Compounds
+2 -1
OF2
The compound is neutral, so the
oxidation number of oxygen will
be sufficient to balance out the
two fluorine atoms. What is it?
More Practice with Covalent Compounds
-2
PO4
3-
Since oxygen is the more
electronegative element, it will
have its normal oxidation
number.
More Practice with Covalent Compounds
+5 -2
PO4
3-
The ion has a charge of negative
three, so the oxidation numbers
must add up to the total charge
of the ion. What is it?
More Practice: Ionic Compounds with
Polyatomics
+2
CaSO4
This is an ionic compound, so the
charge of the metal cation is its
oxidation number. What is it?
More Practice: Ionic Compounds with
Polyatomics
+2
CaSO4
The anion is a polyatomic ion,
sulfate, and the charge of sulfate
is what?
So the oxidation numbers of
sulfur and oxygen must add to -2.
More Practice: Ionic Compounds with
Polyatomics
+2
-2
CaSO4
Oxygen is the more
electronegative of the two, so it
keeps its normal oxidation
number. What is it?
More Practice: Ionic Compounds with
Polyatomics
+2 +6 -2
CaSO4
Sulfur and the four oxygen atoms must add to
negative two (the charge of the sulfate anion).
What is the charge on sulfur?
What is the name?
Calcium sulfate.
More Practice: Ionic Compounds with
Polyatomics
Pb(OH)4
This is an ionic compound, so the
charge of the metal cation is its
oxidation number. But this is a
transition metal, so we cannot
know it from its position on the
periodic table.
More Practice: Ionic Compounds with
Polyatomics
+4
Pb(OH)4
But the anion, the hydroxide ion,
carries a charge of negative one. All
four hydroxides are negative one, but
since the compound is neutral, the
oxidation number of lead must
balance it out. What is it?
More Practice: Ionic Compounds with
Polyatomics
+4
-2
Pb(OH)4
Within the anion, oxygen is the
more electronegative of the two
elements, and keeps its normal
oxidation number. What is it?
More Practice: Ionic Compounds with
Polyatomics
+4
-2 +1
Pb(OH)4
Within the hydroxide ion, the oxygen and
hydrogen must add to the charge of the ion, -1.
What is the charge on H?
What is the name?
Lead (IV) hydroxide