Chapter 7
Naming, Empirical Formula,
Molecular Formula and Percent
Composition
7.1 Chemical Names and Formulas
C8H18
8 Carbon atoms 18 Hydrogen Atoms
Al2(SO4)3
2 Aluminum atoms 4 Oxygen atoms 3 of everything in ( )
making 3 Sulfur atoms and
12 Oxygen atoms total
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Monatomic Ions
:: ions formed from a single atom ::
NAMING :: Element Root + -ide
F
Flourine
N
Nitrogen
FFlouride anion
N3Nitride anion
O2- = ?
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Binary Ionic Compounds
Nomenclature :: naming system
Writing the Formula
Naming ::
Al2O3
Name of Cation
Name of Anion
(with –ide ending)
Aluminum
Oxide
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Nomenclature :: The Stock System
Some elements [such as transition metals] form two or more cations with
different charges. The stock system is used to distinguish between the
different ions of an element.
Fe2+  Iron (II)
Fe3+  Iron (III)
 Cu2+ Cl-
CuCl2
Name of Cation + Roman Numeral
Name of Anion
indicating charge
Copper (II)
Chloride
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Polyatomic Ions & Oxyanions
oxyanions :: polyatomic ions that contain oxygen
1 less O than ___ite
has 1 less O than other oxyanion
ClOHypochlorite
has 1 more O than other oxyanion
ClO2
ClO3
Chlorite
Chlorate
1 more O than ___ate
ClO4
Perchlorate
Common Polyatomic Ions:
NO3-
SO42-
CO32-
PO43-
Nitrate
Sulfate
Carbonate
Phosphate
OHHydroxide
NH4+
Ammonium
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Binary Molecular Compounds
NAMING RULES
1. First element does not take a
prefix if it only contributes 1
atom to the compound
2. Second element takes prefix,
drop ending, add –ide
3. The o or a at the end of prefix
is dropped if the element
begins with a vowel
PREFIXES
# atoms
Prefix
# atoms
Prefix
1
mono-
6
hexa-
2
di-
7
hepta-
3
tri-
8
octa-
4
tetra-
9
nona-
5
penta-
10
deca-
P4O10
Prefix [if needed] +
Prefix [determined by # Name of
element
atoms] + root name + -ide
Tetraphosphorus
decoxide
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
Naming Acids
Have O ?
Yes
No
Hydro________ic Acid [Hydro + root + ic
Ex: HCl Hydrochloric acid
HF Hydrofluoric acid
Poly atomic ion root + suffix Acid
HNO3 Nitric Acid
Nitrate  Nitric Acid
HNO2
HClO4
HClO2
HClO3
Nitrous Acid
Perchloric Acid
Hypochlorous Acid
Chloric Acid
Acid]
ACID SUFFIXES
Polyatomic Ion suffix
Acid suffix
- ate
[nitrate]

-ic [nitric]
-ite
[nitrite]

-ous [nitrous]
Chemical Names & Formulas
Oxidation Numbers
Using Chemical Formulas
Determining Chemical Formulas
Questions
7.2 Oxidation Numbers
Oxidation number :: numbers assigned to compound or ion to indicate the
general distribution of electrons among the bonded atoms in a molecular
compound/ion
Oxidation numbers are helpful in naming compounds, writing formulas, and balancing chemical
equations [redox!!]
Chemical Names & Formulas
Oxidation Numbers
Determining Chemical Formulas
Using Chemical Formulas
Questions
Rules for Assigning Oxidation Numbers
1.
2.
3.
4.
5.
6.
7.
8.
Atoms in pure element have oxidation number zero (0).
Elements in a binary molecular compound are given oxidations numbers equal to the
charges they would have as ions
Flourine always has an oxidation number of -1.
Oxygen has an oxidation number of -2 in every compound except for peroxides (like
H2O2), where it is -1, and with halogens, has oxidation number +2 (OF2)
Hydrogen has oxidation number +1 in compounds with elements more
electronegative than itself; it has oxidation number -1 in metal compounds
Algebraic sum of oxidation numbers of all atoms in compound add up to charge of
compound
Monatomic ions have oxidation numbers equal to their charges.
Rules 1-7 apply to covalently bonded atoms, but oxidation numbers can also be
assigned to atoms in ionic compounds.
Chemical Names & Formulas
Oxidation Numbers
Determining Chemical Formulas
Using Chemical Formulas
Questions
Assigning Oxidation Numbers
UF6
We know that fluorine has oxidation # -1. There are 6 F atoms, so -1 x 6 = -6.
Also, the sum of oxidation numbers must equal the charge of the compound, or O,
in this case. U + (-6) = 0. Therefore, the Oxidation number of U = +6.
Oxidation Number: U: +6 F: -1
ClO3-
Oxygen has oxidation # of -2. Total of oxidation numbers must add up to -1.
Therefore, Cl has oxidation number of +5.
Oxidation Number: Cl: +5 O: -2
Oxidation number S in H2SO4 ??
Answer: +6
Chemical Names & Formulas
Oxidation Numbers
Determining Chemical Formulas
Using Chemical Formulas
Questions
7.3 Using Chemical Formulas
Formula Mass :: sum of the average atomic masses of all the atoms represented
in its formula
FOR EXAMPLE :
The formula mass for H2O is:
Average atomic mass for H : 1.01 amu
Average atomic mass of O : 16.00 amu
2 H atoms x 1.01 amu = 2.02 amu
1 O atom x 16.00 amu = 16.00 amu
formula mass of H2O = 18.02 amu
Chemical Names & Formulas
Oxidation Numbers
Determining Chemical Formulas
Using Chemical Formulas
Questions
Formula Weights
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Formula Weight (FW)
• A formula weight is the sum of the atomic
weights for the atoms in a chemical
formula.
• So, the formula weight of calcium chloride,
CaCl2, would be
Ca: 1(40.1 amu)
+ Cl: 2(35.5 amu)
111.1 amu
• Formula weights are generally reported for
ionic compounds.
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Molecular Weight (MW)
• A molecular weight is the sum of the
atomic weights of the atoms in a molecule.
• For the molecule ethane, C2H6, the
molecular weight would be
C: 2(12.0 amu)
+ H: 6(1.0 amu)
30.0 amu
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Percent Composition
One can find the percentage of the mass of
a compound that comes from each of the
elements in the compound by using this
equation:
(number of atoms)(atomic weight)
x 100
% element =
(FW of the compound)
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Percent Composition
So the percentage of carbon in ethane is…
(2)(12.0 amu)
%C =
(30.0 amu)
=
24.0 amu
x 100
30.0 amu
= 80.0%
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Chemical Formulas
The subscript to the right of
the symbol of an element
tells the number of atoms
of that element in one
molecule of the compound.
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Types of Formulas
• Empirical formulas give the lowest wholenumber ratio of atoms of each element in a
compound.
• Molecular formulas give the exact number of
atoms of each element in a compound.
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Finding Empirical
Formulas
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Calculating Empirical Formulas
One can calculate the empirical formula from the
percent composition.
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Calculating Empirical Formulas
The compound para-aminobenzoic acid (you may have seen it listed as PABA on
your bottle of sunscreen) is composed of carbon (61.31%), hydrogen (5.14%),
nitrogen (10.21%), and oxygen (23.33%). Find the empirical formula of PABA.
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
Assuming 100.00 g of para-aminobenzoic acid,
C:
61.31 g x
H:
5.14 g x
N:
10.21 g x
5.105 mol C
1=mol
12.01 g
= 5.09 mol H
1 mol
1.01
g
= 0.7288
mol N
23.33 g x
1 mol
= 1.456
14.01
g mol O
O:
1 mol
16.00 g
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
Calculate the mole ratio by dividing by the smallest number of moles:
C:
H:
5.105 mol
0.7288 mol
5.09 mol
0.7288 mol
N:
O:
= 7.005  7
= 6.984  7
= 1.000
0.7288 mol
0.7288 mol
= 2.001  2
1.458 mol
0.7288 mol
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Calculating Empirical Formulas
These are the subscripts for the empirical formula:
C7H7NO2
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Molecular Formula
Actual ratio of atoms in a compound.
Ex. H2O, C6H12O6
To determine the molecular formula, divide the molar mass by empirical formula
mass. This will give the number of empirical formula units (n) in actual molecule.
n= Molar Mass/ Empirical Formula Mass
Ex. Determine the empirical and molecular formula of each of the following:
1.Ethylene glycol, the substance used as antifreeze has 38.70 % C, 9.70 % H
and 51.60 % O , mm= 62.10 g
2.Caffeine, a stimulant in coffee has the following percent composition:
49.50 % C, 5.15% H, 28.90 % N and 16.50 % O , molar mass= 195.00g