Determining Formulas
The Criss-Cross Method
 Examples
 Na+1 + O-2

 Ca+2 + P-3 
 C+4 + O-2 
Na2O
Ca3P2
C2O4  reduced to CO2
1
Naming Compounds
 Chemical Nomenclature--> system
used to name chemical substances.
 The Name of a compound indicates
the composition of the substance.
From the name one can
deduce a chemical formula.
2
Naming Binary Compounds
 The first element is named as usual but
only a stem of the second is used followed
by the suffix “ide”
 For example: MgCl2 is Magnesium chloride
: Al2O3 is Aluminum Oxide
 The Chlorine and Oxygen must change their
suffix from “ine” and “ygen” to “ide” !
3
Naming Compounds

Try these!
1. NaCl
2. Li3N
3. MgI2
Sodium Chloride
Lithium Nitride
Magnesium Iodide
4
Stock System
for Transitional Metals
 A compound that contains a transitional
metal must be named so that the oxidation
# of the metal is identified.
 A Roman numeral is placed after the metal.
It represents the oxidation # of the
metal.
Ex.
FeCl3  Iron (III) Chloride
CuCl2  Copper (II) Chloride
5
Assigning Oxidation #
Transitional Metals
 The total charge on any compound or molecule
is always equal to zero.
 To determine unknown oxidation #s, add up the
oxidation #s of the Cation and Anion and set them
equal to zero. (Create an algebra formula and solve for X.)
Example Cr2O3 total charge = 0
Cr = x , O = -2
Formula 2x + 3(-2)= 0  2x-6= 0 x= +3 Cr= +3
6
Naming Transitional
Metal Compound
Name These,
1) FeCl2
2) CrO2
3) NiP
Iron(II) Chloride
Chromium(IV) Oxide
Nickel(III) Phosphide
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Common Names  The old naming system
Latin Names
Antimony
Copper
Sb
Cu
Stibium
Cuprum
Gold
Iron
Lead
Au
Fe
Pb
Aurum
Ferrum
Plumbum
Mercury
Potassium
Silver
Hg
K
Ag
Hydragyrum
Kalium
Argentum
Sodium
Tin
Tungsten
Na
Sn
W
Natrium
Stannum
Wolfram
8
Naming Molecules
(Using prefixes)
 If two non-metals are bonded covalently, the name
can be shown using prefixes.
 The number of atoms for each element in a
molecule is usually indicated by the prefix:
–
–
–
–
–
mono
di
tri
tetra
penta
- 1 atom
- 2 atoms
- 3 atoms
- 4 atoms
- 5 atoms
- hexa
- hepta
- octa
- 6 atoms
- 7 atoms
- 8 atoms
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Naming Molecules
 Examples:
 nitrogen dioxide is NO2
 dinitrogen pentoxide is N2O5
 phosphorus tribromide is PBr3
 The prefix represents the subscript.
 If the subscript is one mono is not needed.
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Binary Molecules
Name these :::
Use Old Naming system and Stock system
1.
PCl3
Phosphorus TriChloride
2.
PCl5
Phosphorus PentaChloride
3.
SO2
Sulfur Dioxide
Phosphorus(III) Chloride
Phosphorus(V) Chloride
Sulfer (IV) Oxide
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Poly-Compounds
 Formulas of compounds containing
polyatomic ions are written in a
manner to stress the fact that the
ions are independent units
 An example is Sodium Nitrate which
contains the nitrate ion (NO3)-1 is
written NaNO3
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POLY-ATOMIC IONS
Poly-atomic ions
Two or more atoms
covalently bonded
but as a group carry
a charge.
Pg 226 lists many
more poly-atomic
ions
Memorize ions.
Formula
Name
(NH4)+1
Ammonium
(C2H3O2)-1
Acetate
(ClO3)-1
Chlorate
(CN)-1
Cyanide
(OH)-1
Hydroxide
(HCO3)-1
Bicarbonate
(NO3)-1
Nitrate
(CO3)-2
Carbonate
(CrO4)-2
Chromate
(O2)-2
Peroxide
(SO4)-2
Sulfate
(PO4)-3
Phosphate
13
Poly-Compounds
 When naming these compounds the name of
the poly-ion is unchanged.
Examples
1. Na2SO4  Sodium Sulfate
2. (NH4)2Se  Ammonium Selenide
If Ammonium is the poly-atomic ion, the
non-metal still maintains its “ide” suffix.
14
Poly-Compounds
 If a compound contains a polyatomic
ion with a subscript of two or more
the ion is enclosed in parenthesis:
 Example:
– calcium bicarbonate Ca(HCO3)2
– ammonium sulfide (NH4)2S
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Poly-Compounds

Name these ::: Go to page 226 or your packet for help.
1.
Ca(ClO3)2
2.
NH4OH
3.
Cr(SO4)2
Calcium Chlorate
Ammonium Hydroxide
Chromium(IV) Sulfate
Memorize the 12 Common Poly-atomic Ions.
There will be an Ion quiz very soon.
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Oxy-Ions
 Polyatomic Ions containing Oxygen can be
represented a number of different ways.
If one less Oxygen in the formula. The suffix is changed
from “ate” to “ite”. The ion’s charge does not change.
Ex.
(NO3)-1  Nitrate vs. (NO2)-1  Nitrite
If two less Oxygens the prefix “hypo-” is placed in front of
the “ite” name.
Ex.
(ClO)-1  hypo- Chlorite
If one more Oxygen the prefix “per-” is placed in front of the
“ate” name.
Ex.
(ClO4)-1  Per Chlorate
17
Acids
Acids have their own naming system and they must be
recognized when dealing with nomenclature.
The name acid comes from the Latin term for “sour”
{Acids are sour to the taste}
Acids are substances that donate protons (H+)
{usually when dissolved in water}
The Chemical formula almost always begins with
Hydrogen
Example: hydrochloric acid  HCl
sulfuric acid  H2SO4
Naming Acids
Lets separate acids into 2 types:
Acids that contain oxygen
H3PO4
HNO3
H2SO4
H2O
Acids that do not contain oxygen
HCl
HF
HBr
H2S
Naming Acids
Naming acids containing oxygen:
For acids containing “-ate” anions:
1. Use root of the anion (for sulfate, SO42-, use sulfur)
2. Add “-ic” suffix then end with “acid”
Example:
H3PO4 is Phosphoric acid
For acids with “-ite” anions:
1. Use root of the anion (for sulfite, SO32-, use sulfur)
2. Add “-ous” suffix then end with “acid”
Example:
H2SO3 is sulfurous acid
Naming Acids (cont.)
Naming acids not containing oxygen:
– Add “hydro-” prefix to beginning
– Use root of the anion (i.e. Cl- use chlor)
– Add “-ic” suffix then end with “acid”
Example:
HCl is hydrochloric acid
Name the following acids:
HF
HNO2
HCN
H3PO4
Hydrate Molecules
 A hydrate molecule is a ionic compound
that contains water molecules trapped
inside the crystalline structure.
The Formula includes a dot followed by
the number of water molecules
Ex: Copper(II) Sulfate Pentahydrate
CuSO4
· 5H O
2
Hydrate Molecules
The Name of a hydrate molecule would
include two separate names.
To name, use the name of the ionic compound
followed by the term … hydrate. A Greek
Prefix would be used to represent the number
of water molecules that are trapped.
CoCl2 · 2 H2O
Colbalt(II) Chloride Dihydrate