Molecular Compounds
Numerical prefixes used for molecular compounds.
1
2
3
4
5
6
mono
di
tri
tetra
penta
hexa
Molecular Compounds: Naming
1. Look at the formula of the molecular compound: CO 2 , Use the periodic table to name the first
element.
C = Carbon
2. Choose the correct prefix for the number of atoms of the element. i.e.
carbon (1 atom of carbon so prefix is mono, but is not included for the 1st element.)
3. Use the periodic table to name the second element.
O = oxygen
4. Change the ending of the second element to “ide”.
oxygen → oxide
5. Choose the correct prefix for the number of atoms of the element.
2 = di → dioxide (2 atoms of oxygen, so prefix is “di”)
6. Combine the two parts of the name.
carbon dioxide
It is important to note that these rules for naming do not apply to a large group of molecular
compounds called organic compounds.
Write the chemical name for the following molecular compounds.
Chemical Formula
SO 2
SO 3
CCl 4
PCl 5
CO
Chemical Name
Molecular Compounds: Writing Chemical Formula
Follow these steps to write the chemical formula of a molecular compound from its name.
dinitrogen tetroxide, N 2 O 4
1. Look at the name of the molecular compound: dinitrogen tetroxide. Use the periodic
table to find the symbols for the elements.
nitrogen = N
oxide = oxygen = O
2. Use the prefixes in the name to determine the number of atoms of each element.
di – 2
two nitrogen = 2N
tetra = 4
four oxygen = 4O
3. Write in the subscripts, and write the chemical formula.
N2O4
Write the chemical formula for each of the following molecular compounds.
Chemical Name
sulphur difluoride
nitrogen monoxide
disulfur trioxide
disulfur trioxide
disulfur difluoride
silcon tetrachloride
diphosphorus pentoxide
carbon disulfide
carbon tetraiodide
dinitrogen tetrasulfide
Chemical Formula
Identify the following compounds as ionic or molecular and write the chemical formula.
Chemical Name
calcium oxide
dinitrogen triiodide
sodium phosphide
iodine trichloride
phosphorus pentabromide
aluminum phosphide
Ionic or Molecular
Chemical Formula