Chem 20
Molecular Compounds
Ionic compounds form with an exchange of electrons between a
metal and a non-metal. Molecular compounds form by the
SHARING of electrons between two __________________. If a chlorine atom is seeking an electron
it will find another ______________ atom and each atom will _________ one of its electrons with
the other. This means that each atom keeps all of its own electrons but one of its electrons is
shared with the other atom. Molecular compounds are normally __________ or __________ at
room temperature. A bond formed by the sharing of electrons is also called a _______________
_______. Examples are CO2 and ammonia (NH3).
Draw a diagram of a chlorine molecule (Cl2), showing how each chlorine atom shares an electron to
form a complete outer shell of electrons:
You try it: Draw a diagram of a methane (CH4) molecule. How do you think the atoms come
together so that each has a stable (full) valence shell?
Chem 20
Combining Capacity:
The number of _____________ that a non-metal needs to share to become stable is a clue to the
number of ________________ bonds it can form. The number of covalent bonds that a non-metal
will have to form to create a __________ molecule is referred to as the atom’s ________________
______________. For example, carbon has _____ electrons in its valence shell. Carbon therefore
“gains” 4 electrons by ____________; carbon has a combining capacity of 4. The following table
contains combining capacities of several common non-metals:
4
3
2
1
H
C
N
O
You try it: Predict the combining capacities of the following non-metals:
F
S
P
Si
Cl
Diatomic Elements:
Recall the first example in this set of notes where we looked at Cl2, a chlorine molecule. Several
elements actually exist like this in __________ as _____________ ______________. Chlorine is
one example, but there are ____ others as well. The following table will tell you which elements
are diatomic, but there is an easier way to remember: Look at the periodic table and notice that
the diatomic elements basically form a __________ gun with a hydrogen bullet and they will be
easier to remember!
Hydrogen
H2
Gas
Oxygen
O2
Gas
Nitrogen
N2
Gas
Fluorine
F2
Gas
Chlorine
Cl2
Gas
Chem 20
Bromine
Br2
Liquid
Iodine
I2
Solid
Naming and Formulas for Molecular Compounds
Rules for Naming:

Write the name of the first element of the formula in full

Change the ending of the second element’s name to “ide” (same as ionic binary compounds)

Use prefixes to indicate the number of atoms of each element in the molecular formula
Note: If the number of atoms in the first element is one, the prefix “mono” is not necessary
Ex - Write the name of the molecular compound P2Cl5
Rules for Formulas:

Molecular compounds are pretty easy: Just read the name of the compound and use the
prefixes to determine the number of atoms of each element.
Ex - Write the formulas of the following molecular compounds: Carbon monoxide, Dinitrogen Tetraoxide
Chem 20
Here are prefixes that will be helpful to you:
mono-
1
di-
2
tri-
3
tetra-
4
penta-
5
hexa-
6
hepta-
7
octa-
8
nona-
9
deca-
10