Lesson 6 Molecular Compounds - Naming and Formulas
Naming Molecular Compounds
Did you know that the main constituent compound to make glass is sand?
B6.4 Hourglass with sand
Sand and glass are both composed of silicon dioxide (SiO2). Silicon dioxide is a molecular compound and can be recognized as such because it is composed of two non-metallic elements: silicon and oxygen. Notice that the name utilizes the prefix
“di.” This is one of the key differences between ionic nomenclature and molecular nomenclature. In molecular nomenclature, prefixes are used to indicate the number of atoms of each element in the molecule.
| Number of Atoms |
Prefix |
|---|---|
| 1 | mono |
| 2 | dri |
| 3 | tri |
| 4 | tetra |
| 5 | penta |
| 6 | hexa |
| 7 | hepta |
| 8 | octa |
| 9 | nona |
| 10 | deca |
Guidelines for naming molecular compounds:
Note: Usually the element that is located farthest to the left on the periodic table is listed first.
Note: Double vowels are not eliminated; e.g., tetraoxide, triiodide, etc., with the exception for monoxide.
- First element name remains unaltered.
- For the second element in the compound, the name ending changes to “ide.”
- Prefixes are added to indicate the number of atoms of each element in the compound. The one exception is that the prefix “mono” is not used when the first element has one atom. Prefixes are used in all other cases.
- Recall that compound names are not proper nouns, so no capital letters are used.
Note: Usually the element that is located farthest to the left on the periodic table is listed first.
Note: Double vowels are not eliminated; e.g., tetraoxide, triiodide, etc., with the exception for monoxide.
Examples
Work through the following examples to help solidify your understanding of molecular nomenclature. Each example has a video to go with it. To play the video, click on the play icon next to the example.
Identify the type of compound.
P—non-metal
Cl—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
Cl—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
For the second element in the compound, the name ending changes to end “ide.”
Cl is chlorine; change ending to “ide”—chloride.
Add appropriate prefix for first element.
Only one P atom, so there is no prefix—phosphorous.
Only one P atom, so there is no prefix—phosphorous.
Add appropriate prefix for second element.
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There are three chlorine atoms, so use the prefix “tri”—trichloride
There are three chlorine atoms, so use the prefix “tri”—trichloride
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/9hh6atyl0s
Identify the type of compound.
N—non-metal
O—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
O—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
For the second element in the compound, the name ending changes to end “ide.”
O is oxygen; change ending to “ide”—oxide.
Add appropriate prefix for first element.
There are two nitrogen atoms, so add the prefix “di”—dinitrogen.
There are two nitrogen atoms, so add the prefix “di”—dinitrogen.
Add appropriate prefix for second element.
There is one oxygen atom, so use the prefix “mono”—monoxide.
There is one oxygen atom, so use the prefix “mono”—monoxide.
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/d16kqzmb9m
Identify the type of compound.
Si—non-metal
H—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
H—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
For the second element in the compound, the name ending changes to end “ide.”
H is hydrogen; change ending to “ide”—hydride.
Add appropriate prefix for first element.
There are two Si atoms, so used the prefix “di” —disilicon.
There are two Si atoms, so used the prefix “di” —disilicon.
Add appropriate prefix for second element.
There are six hydrogen atoms, so use the prefix “hexa”—hexahydride.
There are six hydrogen atoms, so use the prefix “hexa”—hexahydride.
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/arwog1ambt
Identify the type of compound.
S—non-metal
O—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
O—non-metal
Since two non-metals are bonded together, this is a molecular compound and prefixes will be used in the name.
For the second element in the compound, the name ending changes to end “ide.”
O is oxygen; change ending to “ide”—oxide.
Add appropriate prefix for first element.
Only one S atom, so there is no prefix—sulfur.
Only one S atom, so there is no prefix—sulfur.
Add appropriate prefix for second element.
There are two oxygen atoms, so use the prefix “di”—dioxide.
There are two oxygen atoms, so use the prefix “di”—dioxide.
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/6o2pugbjrt
Read This
Please read pages 48 and 49 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on naming molecular compounds. Remember,
if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice
questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.- Provide the correct IUPAC name for each of the following compounds.
P4S7 ClF5 N2O4 O3F2 Si3N4
P4S7 tetraphosphorus heptasulfide CIF5 chlorine pentafluoride N2O4 dinitrogen tetraoxide O3F2 trioxygen difluoride Si3N4 trisilicon tetranitride