Chemistry
Molecular Compounds
MOLECULAR COMPOUNDS
(COVALENT COMPOUNDS)
Covalent Bonds - Video
Ionic Compounds Review
Ionic compounds are the
combination of ions.
E.g. Na+ + Cl-  NaCl.
• This formula represents the
RATIO of sodium ions and
chloride ions not the exact
number of them.
• They are composed of a metal
and a non-metal 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 NONMETALS
Some examples
• N2O
 Nitrous oxide = Gas used at the
dentist to relax patients
• NO2
 Nitrogen dioxide = poisonous
toxin emitted from car exhaust
Hopefully your dentist doesn’t
get them mixed up
More Examples
• H2O
 Water
• CO2
 Carbon Dioxide = Gas
exhaled and created during
combustion reactions
• CO
 Carbon Monoxide = 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 covalent
compounds.
Molecular Compounds
• Share
electrons (e-) to form
a stable arrangement.
• Negative
e- are attracted
to the Positive nuclei of
both atoms
•
This causes them to attract
•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 one more
electron to become stable.
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
F
F
F
Shared
electron pair 
both now have
8 in outer orbit
Molecular Compounds
Many molecular compounds are
predictable.
How will Oxygen bond with Hydrogen
to form a molecule.
Draw the Lewis Structure of both
Atoms.
Oxygen wants to share two electrons
and Hydrogen wants to share one.
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?
C
O
Draw the Lewis Structures of each atom.
Carbon wants to share 4
Oxygen wants to share 2.
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.
O
C
O
Carbon Dioxide
C
O
Carbon
Monoxide
Types of Bonds
H
H O
C
Water – Single
bond because
ONE pair of
electrons are
shared
O
C
O
Carbon Monoxide –
Triple Bond because
THREE pairs of electrons
are shared
O
Carbon Dioxide – Double bond
because TWO pairs of electrons are
shared
Ionic vs. Molecular Videos
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
Mono
2
Di
3
Tri
4
Tetra
5
Penta
6
Hexa
7
Hepta
8
Octa
9
Nona
10
Deca
Note, the mono is omitted on
the first atom.
CO
Carbon Monoxide
CO2
Carbon Dioxide
Naming Example
• P4O10
Phosphorus - use prefix tetra (4)
Oxygen – change ending – Oxide
Oxide – use prefix deca (10)
=tetraphosphorus decaoxide
Writing Formulas
The left-most element goes first
Carbon monoxide
- Carbon (C)  no prefix therefore = C
- Monoxide – Mono = 1 therefore, 1
oxygen atom = O
= CO
Writing Formulas
• Nitrogen
dioxide
- Nitrogen (N)  no prefix therefore = N
- Dioxide – Di = 2 therefore, 2 oxygen atoms
(O2)
= NO2
•Writing Formulas
DiCarbon Tetrahydride
- Dicarbon (C)  Di = 2 therefore = C2
- Tetrahydride (H)  Tetra = 4 therefore, 4
Hydrogen atoms = H4
= C2H4
•Molecular Compounds - Naming
Name the following
compounds
CF4
Carbon Tetrafluoride
H2O
Dihydrogen Monoxide
PF5
Phosphorous Pentafluoride
Write the chemical formula for,
Sulphur Dioxide
SO2
DiCarbon Tetrahydride
C2H4
A THOUSAND BONDS
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 – When two
atoms of the same type
form a covalent molecule,
the result is often a
colorless odorless gas.
Molecular Compounds –
Diatomic Gases
The Halogens, Oxygen, Nitrogen and
Hydrogen form diatomic gases.
H2 is called Hydrogen Gas not Dihydrogen.
Eg. N2 - nitrogen gas
O2 - oxygen gas
Exceptions that need to be
Memorized!
CH4 – methane
H2O2 – hydrogen peroxide
H2O – Water
These Too!
NH3 – ammonia
O3 – Ozone