Warm-Up: To be turned in
 Write the chemical formula for magnesium
chloride.
Chemical Names and Formulas
Molecular Compounds
Molecular compounds
Number
Prefix
compounds in a variety of
proportions
1
Mono-
2
Di-
 Ex: NO, NO2, N2O
3
Tri-
4
Tetra-
5
Penta-
6
Hexa-
7
Hepta-
8
Octa-
9
Nona-
10
Deca-
 Nonmetals can form molecular
 How do we tell them apart?
 We use a system of prefixes to
identify how many of each atom
there are in the compound.
Naming Molecular Compounds
 Write the less electronegative element first. Do not give it a
prefix unless there is more than one of that element.
 The second element is named by combining a prefix
indicating the number of atoms of that element, the root of
the name of the second element, and the ending -ide.
 The o or a at the end of a prefix is usually dropped when the
word following the prefix begins with another vowel, e.g.,
monoxide or pentoxide.
Molecular Compound Examples
 CCl4 = carbon tetrachloride
 N2O5 = dinitrogen pentoxide
 OF2 = oxygen difluoride
 Notice that the prefixes in the names correspond to the
numbers written in the subscripts
 The subscripts in a chemical formula indicate the number of
that atom in a compound
Assigning Oxidation Numbers
 The more electronegative of the two elements will have an
oxidation number which is the same as the charge of its most
common anion
 The less electronegative element will have an oxidation
number that is positive in value
 The algebraic sum of the oxidation numbers will be zero.
Oxygen is the more electronegative
element, so it is assigned an oxidation
number of -2
Example
The algebraic sum of all
oxidation numbers must equal
zero.
(5▪-2) + (2▪x)= 0
-10 + 2x= 0
2x= 10
X=5
Thus, each nitrogen has an
oxidation number of +5
+5
-2
+10
-10
N2O5
There are 5 oxygen atoms. This makes
a total oxidation number of -10
Homework
Name the following compounds
using the prefix system.
 CO2
 SeF6
 CCl4
 As2O5
 PCl5
Write the formula for the
following compounds.
 carbon tetrabromide
 silicon dioxide
 tetraphosphorus decoxide
 diarsenic trisulfide
 Dihydrogen monoxide