Naming Molecular Compounds

Nomenclature (Naming):  Binary Molecular Compounds
Dr. MJ Patterson

 

Different classes of compounds have different rules for naming.  Before naming a compound, it is important to check which class it belongs to so that you will use the appropriate set of rules.

To use this set of rules, the compound must be molecular.  In other words, it must be a nonmetal + a nonmetal (Refer to Module 3 - The Periodic Table.  The nonmetals are in the upper right corner of the periodic table, to the right of the metalloids.).

  1. Name the first element as the element.
    2.    Name the second element with an -ide ending.
    3.    Use numerical prefixes to specify how many of each atom is present in the molecule.  Mono is frequently omitted.  Memorize these prefixes!

     

Prefix

Number

mono

1

di

2

tri

3

tetra

4

penta

5

hexa

6

hepta

7

octa

8

nona

9

deca

10

Example 1:
Name NH3 and H2O.

Solution 1:
Gotcha!  These are ammonia and water.  They are always referred to by their common names.

Example 2:
Name P2O5.

Solution 2:
Two phosphorus atoms means we use the di prefix.  Five oxygens requires penta.  The second element, or oxygen, gets the -ide ending.
Diphosphorus pentoxide.

Example 3:
Write the formula for dinitrogen tetroxide.

Solution:
Dinitrogen means there are two nitrogens, so there will be a subscript of 2 after the N.  Tetroxide means there are 4 oxygens, so there will be a 4 after the O.
N2O4