Molecular Compounds (a.k.a.
Covalent Compounds)
Ionic Compounds Review
• Ionic compounds are the combination of
ions. E.g. Na+ + Cl-  NaCl.
• This formula represents the __________
of sodium ions and chloride ions not the
exact number of them.
• They are composed of a
___________________ and form a crystal
structure (e.g. NaCl and CaCl2 which are
both salts)
Molecular Compounds
• Consist of atoms covalently bonded
together
• The elements involved are all __________
Some examples
• N2O  _____________ = Gas used at the
dentist to relax patients
• NO2  _____________ = poisonous toxin
emitted from car exhaust
More Examples
• H2O  ______
• CO2  ____________ = Gas
exhaled and created during
combustion reactions
• CO  ____________________= Lethal
gas created during incomplete combustion
Recall
• In ionic compounds, the non-metal rips
away the electron(s) from the metal
because the metals loosely hold their
electrons
• This creates a positive and negative ion
which attract each other making them stick
together (opposites attract)
Molecular Compounds
• made up of a non-metal
and a non-metal.
• also called _____________
Molecular Compounds
• ________ electrons (e-) to
form a ________________.
• Neg. e- are attracted to the
Pos. nuclei of both atoms
Molecular Compounds
Molecular compounds are formed
when non metals share
electrons to fill their outer
electron orbit (shell).
If we draw the Lewis Structure for
Fluorine,
We can see that it needs
________
F
F
F
It wants to share one electron with
another atom.
If it bonds with another fluorine
atom
We draw the shared pair of
electrons between the two
atoms.
F
Shared electron
pair  ______
Molecular Compounds
Many molecular compounds are
predictable.
How will Oxygen bond with
Hydrogen to form a molecule.
Draw the Lewis Structure of both
Atoms.
________________________
H
H
O
H
H O
Clearly we need another
Hydrogen atom
Putting the shared electrons
between the atoms.
The molecule is H2O
**The Oxygen atom has 8
valence electrons (full) and
the Hydrogen has 2 valence
electrons (full)
Molecular Compounds
Not all molecular compounds are
as predictable.
How will Oxygen bond with
Carbon?
Draw the Lewis Structures of
each atom.
___________________________
C
O
C
O
O
_____________
If we add one more Oxygen, each
oxygen can share two.
However, if Oxygen will share two
and donate one of its other
electrons pairs, Oxygen can
bond with just on Carbon atom.
C
O
_____________
H
Types of Bonds
H O
C
Water – Single
bond because
______ pair of
electrons are
shared
O
O
O
Carbon Monoxide – Triple
Bond because
_______pairs of electrons
are shared
C
Carbon Dioxide – Double bond because
_______pairs of electrons are shared
Molecular Compounds –
Naming
So Oxygen can form CO or CO2
We need a more flexible naming
system for covalent
compounds to reflect the
many different bonding
possibilities.
To name a covalent compound,
1. Starting with the atom that is
to the left in the periodic
table, (or lower)
2. Write the name of the atoms
with the prefix indicating the
number of that atom in the
compound.
3. Change the ending of the last
atom to – ide.
The prefixes are,
1
_______
2
_______
3
_______
4
_______
5
_______
6
_______
7
_______
Note, the mono is omitted on the
first atom.
CO
_____________
CO2
_____________
Memorize me!
Number
Prefix
Number
Prefix
1
mono
6
_________
2
_________ 7
hepta
3
tri
_________
4
_________ 9
nona
5
penta
_________
8
10
Naming Example
• P4O10
Phosphorus - use prefix tetra (4)
Oxygen – change ending – Oxide
Oxide – use prefix deca (10)
= _________
Molecular Compounds - Naming
Name the following compounds
Write the chemical formula for,
CF4
Sulphur Dioxide
_________
_________
H 2O
_________
DiCarbon Tetrahydride
_________
PF5
_________
Molecular Compounds – Diatomic
Gases
Molecular compounds show an
incredible variety in structure,
physical and chemical
properties.
There are categories that further
divide covalent compounds
into categories with common
properties.
Diatomic Gases – _________
The Halogens, Oxygen, Nitrogen
and Hydrogen form diatomic
gases.
H2 is called Hydrogen Gas not
Dihydrogen.
Eg. N2 - _________
O2 - _________
Air
Writing Formulas
left-most element goes 1st
Carbon monoxide
- Carbon (C)  no prefix therefore = C
- Monoxide – Mono = 1 therefore, 1 oxygen
atom = O
= _________
Writing Formulas
• Nitrogen dioxide
- Nitrogen (N)  no prefix therefore = N
- Dioxide – Di = 2 therefore, 2 oxygen
atoms = O2
= _________
Writing Formulas
DiCarbon Tetrahydride
- Dicarbon (C)  Di = 2 therefore = C2
- Tetrahydride (H)  Tetra = 4 therefore, 4
Hydrogen atoms = H4
= _________
Exceptions that need to be
Memorized!
CH4 – _________
H2O2 – _________
H2O – Water
These Too!
NH3 – _________
O3 – _________