5.10 Molecular
Compounds
What are they? How are they formed?
Molecules and Covalent
Bonding
• A molecular compound is a pure substance
formed from non-metals.
• Involves the sharing of electrons between the
non-metals in order to obtain full electron
orbits.
• Examples include: H2O; CO2; H2
• Covalent Bond
 A shared pair of electrons between
two non-metals that hold the
atoms together
Type of Compounds
Diatomic Molecules
• Molecules made up of two identical
atoms
• Some atoms naturally form
diatomic molecules
• Examples:
H2; O2; Br2; N2; F2; Cl2; I2
• These are all gases – hydrogen
gas (H2); nitrogen gas (N2);
oxygen gas (O2)
• YOU MUST MEMORIZE
THESE!!
Naming Molecular
Compounds
• When naming molecular compounds,
scientists use prefixes to specify the number
of each type of element in a molecule.
• The prefix mono is used only for the second
element in the compound.
Prefix
Number
of
atoms
mon(o) -
1
di -
tri -
2
tetra -
3
4
penta -
5
hexa -
6
hepta -
7
octa -
8
nona -
9
deca -
10
Naming Molecular
Compounds
1. Write the name of the first elements and
change the ending of the second
element to “ide”.
2. Add the prefixes to each element.
(NOTE: The prefix mono- is not
necessary on the first element.)
Example: P2O5 is ________________.
Practice
1. N2O5
__________________
2. SO3
__________________
3. CS2
__________________
4. CO
__________________
Chemical Formulas for
Molecular Compounds
1. Write the symbols for each element in
the compound.
2. Use the prefixes for each element to
determine how many of each element is
found in the molecule and add them to
the symbols using subscripts. (NOTE:
There will be no prefix in the first
element if there is only one.)
Practice
1. phosphorus pentabromide
_________
2. carbon tetrachloride
_________
3. diphosphorus trioxide
_________
4. dinitrogen monoxide
_________
Common Names
• Some molecular compounds are
referred to by their common names.
• Examples:
• H2O – water
• NH3 – ammonia
• H2O2 – hydrogen peroxide
• CH4 – methane
• O3 – ozone
• NO – nitric oxide
• YOU MUST MEMORIZE
THESE!!