Covalent Compounds
This program will help you learn how to
name covalently bonded compounds
and how to write their formulas.
Covalent compounds are formed when two
nonmetals share electrons. Where are the
nonmetals on the periodic table?
That is correct, the nonmetals are on the right side
of the periodic table.
When naming covalent compounds, you list the
name of the most metallic element first. The most
metallic would be the element furthest to the left.
Since electrons are shared and not lost or gained,
we have to have a special method to name these
molecules. For this we use PREFIXES.
For example, here are two common gases you would find in
our air:
CO – this gas is a poisonous product of car exhaust.
CO2 – this gas is exhaled by humans and plants love it.
Can we call both of them carbon oxide? NO, we don’t want
to mix them up, it could be deadly.
PREFIXES
For naming covalent compounds, use the following:
1 - mono
2 - di
3 - tri
Exception: For some reason,
the prefix mono Is not used
4 - tetra
on the first element.
5 - penta
6 - hexa
7 - hepta
Only use prefixes with
8 - octa
covalent compounds.
9 - nona
10 - deca
CO or CO2?
Using our prefixes, we now know that……
CO is carbon monoxide
CO2 is carbon dioxide
Notice the carbon does not have a prefix, mono is not
used on the first element.
The prefix before oxide indicates the number of
oxygen atoms in the compound.
N2O3 What would you call it? Dinitrogen trioxide
Dinitrogen because there are two nitrogen atoms.
Trioxide because there are three oxygen atoms.
PH3 What would you call it? Phosphorous trihydride.
No mono on the first element.
Hydrogen is sometimes a nonmetal, when it is listed last in
compound.