Unit 7.1 Naming Molecular
Compounds
Teacher: Dr. Van Der Sluys
Objectives
• Naming molecular compounds
– Using prefixes
– Stock naming system
Prefixes
• A prefix is a morpheme (portion of a word)
that comes at the beginning of the word and
has a specific meaning
Mono-
one
Penta-
five
Di-
two
Hexa-
six
Tri-
three
Hepta-
seven
Tetra-
four
Octa-
eight
Naming Molecular
Compounds with Prefixes
1. Use a prefix to indicate how many atoms
there are of the first element in the formula,
except if there is only one atom of the first
element, then do not use the prefix mono-.
2. After the prefix, use the name of the first
element in the formula.
3. Use a prefix to indicate the number of
atoms for the second element in the
formula.
4. Use the root of the second elements name
and the suffix -ide.
Examples
•
•
•
•
•
N 2O
NO
NO2
CO2
CO
dinitrogen monoxide
nitrogen monoxide
nitrogen dioxide
carbon dioxide
carbon monoxide
More Examples
•
•
•
•
•
•
CF4
SO2
SF6
Dichlorine heptaoxide
Hydrogen chloride
Phosphorus trichloride
Exceptions
• H 2O
water
• NH3
ammonia
• Organic compounds - compounds
containing carbon bonded to hydrogen
have their own unique naming system
– CH4 methane
– C2H6 ethane
– C3H8 propane
The Stock Naming System
The International Union of Pure and Applied
Chemists (IUPAC) have developed a naming
system based on the oxidation numbers of
the first element in the formula.
1. Name the first element.
2. Use a Roman numeral to indicate the oxidation
number, by reversing the criss-cross and
determining the charge as if it were an ionic
compound.
3. Use the root of the second elements name and end
with the suffix -ide.
Rationale
• In compounds that contain polar covalent
bonds, electrons are displaced towards the
more electronegative atom. This results in
partial positive negative charges. The stock
naming system assumes that the bonding is
ionic rather than covalent.
..
..
O=C=O
..
..
Carbon dioxide
..
..
2- [C]4+ [:O:]2[:O:]
..
..
Carbon (IV) oxide
Example
• CF4
C4+ and F-
Carbon (IV) fluoride
• N2O
N+ and O2-
Nitrogen (I) oxide
• CO2
C4+ and O2-
carbon (IV) oxide
• SF6
S6+ and F-
sulfur (VI) fluoride
Examples
• CO
• NO2
• Phosphorus (V) oxide
• Chlorine (VII) oxide
Summary
• Prefixes are used to indicate the
number of each element in the formula
• Stock naming system uses roman
numerals to indicate the charge of the
first element as determine from the
criss-cross system.