MOLECULAR COMPOUNDS
What are they and how to name
them?
Molecular Compounds
Definition: A compound formed when
atoms of two or more different
elements share electrons
• Usually formed between 2 or more
non-metals and are also called
covalent compounds
Ionic vs. Molecular?
Ionic
Compounds
Molecular
Compounds
How atoms
bond?
Transfer of
electron
opposite charges
attract
Atoms share
electrons to
complete
valence shells
What bonds
with what?
Metal to nonmetal
Non-metal to
non-metal
What do they
form?
Lattice structure
Smaller
(solids)
compounds with
2-3 atoms linked
Ionic
Covalent
Naming Molecular Compounds
Naming molecular compounds is different from
ionic and polyatomic compounds. In molecular
compounds the name uses a prefix to indicate
the number of each atom present.
Example: Carbon Dioxide tells us it is made of
carbon and oxygen in a ratio of 1 carbon atoms
to 2 oxygen atoms.
Prefixes
Prefix
Number of
atoms
Example
mono
1
(CO) carbon monoxide
di
2
(CO2) carbon dioxide
tri
3
(SO3) sulfur trioxide
tetra
4
(CF4) carbon tetrafluoride
penta
5
(PBr5) phosphorus pentabromide
hexa
6
(SF6) sulfur hexafluoride
hepta
7
octa
8
nona
9
deca
10
(P4O10) tetraphosphorous decaoxide
Writing Names
1.
2.
3.
4.
Count the # of atoms of the first element.
Write the prefix for this number followed by
the name of the first element. If there is only
one of the first element we leave out the
prefix.
Count the # of atoms of the second element.
Write the prefix for this number followed by
the name of the element using the suffix –ide.
Examples
N2O4
Nitrogen atoms = 2  dinitrogen
Oxygen atoms = 4  tetraoxide
Full name = dinitrogen tetraoxide
C2F6
Carbon atoms = 2  dicarbon
Fluoride atoms = 6  hexafluoride
Full name = dicarbon hexafluoride
Writing Formulas
1. Write the symbol for the elements.
2. Write the subscript for the number of
atoms represented by the prefix.
3. Notice—the ratio in the formula is not
reduced to its simplest form like ionic
compounds.
Examples
sulfur trioxide
SO3
diphosphorus pentasulfide
P2S5
Diatomic Elements
Some elements are diatomic. This means they exist
naturally as two of the same element bonded
together
Examples:
Hydrogen gas
H2
Bromine liquid
Br2
Oxygen gas
O2
Iodine solid
I2
Nitrogen gas
N2
Fluorine gas
F2
Chlorine gas
Cl2