Molecular Compounds
A molecular compound consists of two non-metals. They are also called
covalent compounds.
Recall:
 Ionic compounds are formed when a metal combines with a non-metal
by the transfer of electrons
 One ion is positive, and the other is negative – therefore they attract
and form an ionic bond
In molecular compounds:
 electrons are shared between elements, NOT transferred
 covalent bonds are formed
Example: H2 – hydrogen gas
H2O – water
Other examples of molecular compounds include:
 O2 – oxygen gas
 NH3 – ammonia
 CH4 – methane gas
 C12H22O11 – table sugar
 H2O - water
 C8H18 – octane
Diatomic Molecules:
 Molecules consisting of two atoms joined by a covalent bond
 Atoms such as oxygen can’t exist alone – will form diatomic molecules
 there are seven diatomic molecules:
H2
N2
O2
F2
Cl2
Br2
I2
Naming Molecular Compounds:
The name of each element begins with a prefix which indicates the number
of atoms of the element.
Naming formula:
Element 1:
prefix + element name
Element 2:
prefix + element stem + -ide
Remember: These rules only apply to two non-metals!
Number
Prefix
Example
Name
1*
mono-*
CO
carbon monoxide
2
di-
CS2
carbon disulphide
3
tri-
SO3
sulfur trioxide
4
tetra-
CF4
carbon tetrafluoride
5
penta-
PBr5
phosphorus pentabromide
6
hexa-
SF6
sulfur hexafluoride
7
hepta-
8
octa-
9
nona-
10
deca-
*Note: mono- is usually omitted from the name of the first element
Examples:
N2O3 – _________________________________________
CCl4 – __________________________________________
trinitrogen pentoxide – _____________
silicon dioxide – _____________