1. Intro to Molecular Compounds
Molecule – smallest electrically neutral unit of a substance that still has the properties of the substance
. . . Basically they are 2 or more non-metallic atoms that act as a unit
Water Molecules

2. Properties of Molecular Compounds
Tend to have low melting / boiling points
Many exist as gas / liquid at room temp.
Poor conductors of electricity
Example: CO2 (Carbon Dioxide)
I love molecular formulas!

3. Te At
Binary Molecular Compounds – Compounds composed of two nonmetallic elements.

4. Important nonmetallic elements that exist as diatomic molecules
I’m Mr. HOFBrINCl
Hydrogen H2
Oxygen O2
Fluorine F2
Bromine Br2
Iodine I2
Nitrogen N2
Chlorine Cl2

5. Naming Binary Molecular Compounds

6. Why is a naming system important?
Carbon and oxygen combine to form carbon monoxide (CO) and carbon dioxide (CO2), but these two invisible gases are very different.
Sitting in a room with small amounts of CO2 in the air would not present any problems. If the same amount of CO were in the room, you could die of asphyxiation. A naming system that distinguishes between compounds is needed.
Carbon monoxide is an invisible, gaseous compound of carbon and oxygen. It is a toxic product of incomplete burning, such as occurs in automobile engines and faulty furnaces.

7. Naming Binary Molecular Compounds
Use prefixes – these tell how many atoms of each element are present in each molecule
My dear tricky twin puts hexes haphazardly on naughty demons
Darn you, you tricky twin!

8. Notes to Know: Te At
The element with more metallic character is named first (the one closer to the stair-step).
Example: CO not OC
Change the ending of the second element to “ide”
O2F2 =
Dioxygen difluoride
(NOT Dioxygen difluorine)
NEVER reduce the subscripts!!

9. NEVER, EVER reduce the subscripts of molecules!!!
Notes to know:
Do not write “mono” if there is only 1 of the first element
CO2 =
Carbon dioxide (NOT Monocarbon dioxide)
SF2 =
Sulfur difluoride (NOT Monosulfur difluoride)
Did I mention...
NEVER, EVER reduce the subscripts of molecules!!!

10. For those who care about spelling...
When a prefix is added that places two vowels next to each other, the ‘a’ or ‘o’ on the prefix is dropped. The ‘i’ in ‘di-’ or ‘tri’ is never dropped.
CO =
carbon monoxide
NOT carbon monooxide
Br2O8 =
dibromine octoxide
NOT dibromine octaoxide
BI3 =
boron triiodide
NOT boron triodide

11. DON’T DO IT!!! Don’t reduce the subscripts!!!
Practice
Write the correct name/formula for:
PCl5
S2Br6 BN
disulfur dichloride
silicon tetrachloride
phosphorus pentachloride
disulfur hexabromide
boron mononitride
S2Cl2
SiCl4
Oh yeah, just one more thing...
DON’T DO IT!!! Don’t reduce the subscripts!!!

12. Practice 1. Which of the following compounds is named INCORRECTLY?
CS2, carbon disulfide
BCl3, boron trichloride
IF7, iodine heptafluoride
PCl5, phosphorus hexachloride

13. Practice
2. Which of the following molecular compounds is named INCORRECTLY?
SbCl3, antimony trichloride
C2O5, dicarbon pentoxide
CF4, carbon tetrafluoride
H3As, hydrogen arsenide

14. Practice 3. The correct formula for tetraphosphorus trisulfide is P3S4