Molecular Compounds

Writing Names and Formulas

Molecular Compounds

Molecular compounds are made of molecules.

They are made by joining nonmetal atoms together into molecules.

Naming is Easier

A molecular compound’s name tells you the number of atoms through the use of prefixes.

Prefixes

1 mono- 2 di- 3 tri- 4 tetra- 5 penta-

6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

Prefixes The name will consist of two words.

Prefix name prefix name -ide

One exception is we don’t write mono- if there is only one of the first element.

Prefixes

The following double vowels cannot be used when writing names:(oa)(oo)

Example

NO2

There is one nitrogen

mononitrogen

But, you cannot use mono- on the first element, so drop the prefix.

mononitrogen nitrogen

Example

NO2

There are two oxygens

dioxygen

Example

NO2

dioxygen

You need the suffix -ide

dioxygenide

Example

NO2

nitrogen dioxide

Example

N2O

There are two nitrogens

dinitrogen

There is one oxygen

monooxygen

Example

N2O

monooxygen

You cannot run (oo) together, so

monoxygen

Example

N2O

monoxygen

You need the suffix -ide

monoxygenide

Example

N2O

dinitrogen monoxide

Problem

Name the following molecular compounds.

Cl2O7

CBr4

dichlorine heptoxide

carbon tetrabromide

Problem

Name the following molecular compounds.

CO2

BCl3

carbon dioxide

boron trichloride

Naming Molecular Compounds

You will not need to criss-cross oxidation numbers.

Molecular compounds name tells you the number of atoms through the use of prefixes.

Example

diphosphorus pentoxide

The name implies there are 2 phosphorous atoms and 5 oxygens.

P2O5

Example

sulfur hexaflouride

The name implies there is 1 sulfur atom and 6 fluorines.

SF6

Problem

Write the formulas for the following molecules. tetraiodide nonoxide

nitrogen trioxide

I4O9

NO3

Problem

Write the formulas for the following molecules. carbon tetrahydride

phosphorus trifluoride

CH4

PF3