Covalent Molecules
EXAMPLE LEWIS
STRUCTURE
HCl
CO2
No lone pair
around the central
atom!
# of connections
+ lone pair
electrons off
central atom
No central atom.
diatomic
molecule
3D DIAGRAM
2 connections
and 0 lone pair
coming off of the
central atom.
2 atoms attached to
central atom
3 connections
and 0 lone pair
coming off of
central atom.
4 connections
and 0 lone pair
coming off of
central atom.
H2O
2 lone pairs around
the central atom!
PCl5
Linear molecules
are generally nonpolar if the 2
atoms are the
same.
Linear molecules
with 3 atoms are
generally nonpolar if the 2
non-central atoms
are the same.
Trigonal Planar
molecules are
non-polar if the 3
non-central atoms
are the same.
180º
Linear
180º
3 atoms attached to
central atom
Trigonal
Planar
120º
4 atoms attached to
central atom
Tetrahedral
109.5º
3 connections
and 1 lone pair
of electrons
coming off of
central atom.
3 atoms attached to
central atom
2 connections
and 2 lone pairs
of electrons
coming off of
central atom.
2,2
5,0
Pyramidal
(Trigonal
Pyramidal)
2 atoms attached to
central atom
107º
Bent or
Angular
ALWAYS
POLAR!
<<109.5º
LONE
ELECTRONS
ON CENTRAL
ATOM.
Trigonal
Bipyramidal
molecules are
non-polar if the 3
non-central atoms
are the same and
the 2 non-central
atoms are the
same (or all 5).
Octahedral
molecules are
non-polar if the 4
non-central atoms
are the same and
the 2 non-central
atoms are the
same(or all 6).
104.5º
Trigonal
Bipyramidal
120º, 180º,
90º
No lone pair
around the central
atom!
SF6
Octahedral
6 connections
coming off of
central atom.
6,0
ALWAYS
POLAR!
LONE
ELECTRONS
ON CENTRAL
ATOM.
<109.5º
3,1
5 connections
coming off of
central atom.
No lone pair
around the central
atom!
Tetrahedral
molecules are
non-polar if the 4
non-central atoms
are the same.
4,0
NH3
1 lone pair around
the central atom!
Linear
3,0
CH4
No lone pair
around the central
atom!
MOLECULAR
POLARITY
2,0
BF3
No lone pair
around the central
atom!
GEOMETRY
/ ANGLE
180º, 90º
1
First: Review Ionic Bonding
TYPES OF BONDING AND PROPERTIES
http://youtu.be/Bjf9gMDP47s (even though it says it is metallic bonding,
the video actually begins with ionic bonding. Since metallic bonding is next in
the packet, watch the entire thing.)
1. IONIC BONDING (Metal + Nonmetal)



Metal + monoatomic ion
Metal + polyatomic ion
Cation + anion
A) In ionic bonding, electrons are ( transferred / shared) to attain a noble gas configuration. This process
turns atoms into ___________.
DEPICTING IONIC BONDING USING LEWIS STRUCTURES: HTTP://YOUTU.BE/K--NQD_MU7O
METAL + NON-METAL
Compounds
Before
Draw Lewis dot structures for the atoms found in the
compound and use arrows to show the transfer of
electron(s)
After
Use brackets around each ion formed and show
the dots ONLY for the NON-METAL. The metal
should have no dots in the “after” picture.
Calcium chloride
(Criss-cross to determine the
formula)
__________________
Aluminum Fluoride
(Criss-cross to determine the
formula)
__________________
B) As a solid, the ions are in (random / fixed) positions. This makes ionic solids very stable, immobile and
they do not_______________ electricity. Ionic solids are brittle. Ionic substances can ___________electricity
when dissolved because ions are free to ___________.
2
C) It is relatively easy to dissolve most ionic solids in water because water is a very polar molecule. It is VERY
difficult to melt or boil an ionic solid. In order to melt or boil an ionic crystal, you must break multiple ionic
bonds. That is very difficult. Have you ever seen salt melt? This is why we can cook with salt and the salt
doesn’t burn. Sugar is different. Sugar melts easily and burns easily. Do you think sugar is an ionic
substance?________
PROPERTIES OF IONIC COMPOUNDS: http://youtu.be/6fam0LZV-8U
1._________________________________________________________________________
2._________________________________________________________________________
3._________________________________________________________________________
4._________________________________________________________________________
5. _________________________________________________________________________
Ex:
2. METALLIC BONDING: http://youtu.be/Bjf9gMDP47s
Ex:




Metals only!
Metals often form lattices in the solid state
Similar to ionic crystal lattices
The metal atoms contribute their valence electrons to a “sea of electrons”
Delocalized electrons - “sea” of mobile electrons
The metallic bond is a bond between valence
electrons and positively charged metal ions!
PROPERTIES OF METALS:
1. Solid at room temperature (except Hg).
2. Luster (shine).
3. Malleable.
4. Ductile.
5. Conducts heat or electricity.
Positive metal
ions in fixed
positions
Mobile Valence
electrons
All because of mobile valence electrons!
3
The rest of this packet will focus on Covalent Bonding!!!!
3. COVALENT BONDING http://youtu.be/-v8XRaVBbDI (video is about drawing but watch it since
drawing comes soon in this packet) https://youtu.be/MlgKp4FUV6I
In covalent bonding, electrons are ( transferred / shared) to attain a noble gas configuration.
non-metals ONLY!
a. Regular COVALENT MOLECULES:
COVALENT MOLECULES : NON-POLAR VS. POLAR MOLECULES
1.
Determining if a molecule is polar: http://www.youtube.com/watch?v=OrLBWWZKmwY
2. polar and non-polar bonds. At end, it shows polar and non-polar molecules - http://youtu.be/un93VJxUfPA
3.
http://www.brightstorm.com/science/chemistry/chemical-bonds/covalent-bonds/
4.
http://youtu.be/S8QsLUO_tgQ
See my web page to copy definitions and properties below:
A) NONPOLAR COVALENT MOLECULE:
Definition:
Properties:
B) POLAR COVALENT MOLECULE:
Definition:
Properties:
TRY: Label the substances below as: metallic, ionic, network covalent, molecular (non-polar) or
molecular (polar).
a. dissolves in water, does not conduct electricity as a solid, but does when dissolved in water_______________
b. dissolves in acetone, low boiling point__________________________
c. shiny, conducts electricity as a solid________________________
d. gas at room temperature______________________________
e. NH3__________________________________
f. NaBr_________________________________
g. CO2__________________________________
4
Almost always
Cl-Cl
H-H
O=O
called a dipole. HF
Depending on the
symmetry. If the
molecule is
symmetrical, then
the polarities cancel
out!!
Non-polar due
to symmetry
4. Symmetrical molecules are non-polar.
The drawings of these molecules are structural formulas. What can you see with a structural formula?
1. __types of a __ __ __ __ in the molecule.
2. __which atoms b __ __ __ to which other atoms
3.__arrangement in space____________________
5
http://youtu.be/uYtwU0uRK7o
1. ENTIRE MOLECULES CAN BE POLAR OR NON-POLAR.
Based on _______________________________________________
_______________________________________________
https://www.youtube.com/watch?v=02Q352-Y7iU
2. INDIVIDUAL COVALENT BONDS CAN BE POLAR OR NON-POLAR
Based on differences in __________________________________ (subtract the values)
Electronegativity Difference Bond Type
0.0 < difference ≤ 0.4
nonpolar covalent
(equal sharing)
0.4 < difference < 1.67
polar covalent
(unequal sharing)
Difference ≥1.67
Ionic (transfer)
1. Use the chart above to classify the following bonds as either non-polar covalent, polar
covalent or ionic.
a. Si-P_________________________
b. H-O_________________________
c. Na-S_________________________
d. C-H_________________________
2. Which bond is the most polar? Least polar?
a. C-C
b. C-Br
c. C-F
6
DRAWING LEWIS STRUCTURES FOR COVALENT MOLECULES:
https://youtu.be/G7crWDN9Q1c
http://youtu.be/Ntwj-Qh12CQ
1. Count the total number of valence electrons (Group/Column #) – Total valence electrons
2. Draw stick figure. Choose a central atom. This is normally the first atom unless the 1st is hydrogen. Then
choose 2nd atom. WHEN IN DOUBT, CARBON IS ALWAYS A CENTRAL ATOM!
Arrange other atoms around central atom. (There may be more than one central atom) and place a BOND
(A LINE) between adjacent atoms to represent SHARED ELECTRONS.
Subtract two electrons for each bond drawn from the total. After subtraction - the # of electrons that you “HAVE”.
3. Count how many electrons each atom “NEEDS” to be stable. (H – 2, most others – 8)
4.
*a. If NEED = HAVE, draw in the electrons as dots.
*b. If NEED > HAVE, draw in 1 multiple bond for each difference of 2 between your NEED and HAVE
BUT, NEVER GIVE A MULTIPLE BOND TO BORON (B), HALOGENS (COLUMN 7) or HYDROGEN (H)!
c. If NEED < HAVE, you may give any extra to the central atom.
7. Draw in the rest of the dots (e-) to complete all octets (except H, He, Be, and B).
Carbon will almost never have dots (electrons) - only bonds (exception)
HINTS:
C
always in the center, always bonds 4x
H, halogens
never in center, always bond 1x
O
unless an ion, bonds 2x
N
usually bonds 3x
HONC - 1234
Example: SiBr4
1. Si  4 valence electrons to offer
Br  4(7) = 28 valence electrons to offer
4 + 28 = 32
2. Stick figure. Central atom  Si
3. Subtract 8 electrons (4 bonds) from the total # of
electrons from #1. This is your “Have”
32-8 = 24 have
4. Calculate your “need”. (Si is fine – it has 8 e
around it but each Br needs 6 more so need is 24e
and we have 24 so add the (dots) electrons.
Final picture

7
http://youtu.be/sceYMpBrNNo
H2O
O2
PF3
6+6=12
draw stick figure
O—O
12-2=10(have)
CH4
Each O needs 6 so need 12.
Difference of 2 between need
and have so draw 1 multiple
bond and then give each
element the dots they need for
an octet
N2
BH3 (Watch it – exception!)
central – B (3,0)
Planar 120°,
Non-Polar
Don’t add another
Bond even if need/
Have tells you to.
CO2
CH2O
HCN
C2H6
C2H4
C2F2
8
SO4-2
ClO3-1
NH4+1
VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) IS BASED ON:
1) Shared and unshared pairs of electrons repel each other yet an unshared pair of electrons repels more
strongly than a shared pair
2) For the purpose of this model, a double or triple bond is considered equivalent to a single bond
3) The shape of a molecule or ion is the result of the shared and unshared pair of electrons being placed as
far from each other as possible
To apply VSEPR, we look at the central atom and count the # of shared and unshared pair of electron
associated with it and this theory is based on placing electrons as far away from each other to minimize
repulsions.
See chart on p1 of packet
Exceptions to the Octet Rule
Rules:





Second row elements C, N, O, F should always be assumed to follow the octet rule
Second row elements Be and B often have fewer than eight electrons and are called electron-deficient.
They are very reactive.
Second row elements never exceed the octet rule since s & p can only have 8 eThird row and heavier elements often satisfy the octet rule but can exceed the octet rule by using their
empty valence d orbitals
If electrons remain, they should be placed on the atom that has a d orbital available and preferably the
central atom.
Ex. PCl5, I3-, ClF3, XeF4, BeCl2, ICl4-
9
Triple Bonds are (stronger / weaker ) and (shorter/ longer ) than double bonds.
They are made of 1_________ and 2 ____ bonds.
Double Bonds are (stronger / weaker ) and (shorter/ longer ) than single bonds. They are made of
1_________ and 1 ____ bonds.
b. Special type of covalent bonding - NETWORK COVALENT BONDING:

atoms are covalently bonded with each other WITHOUT ever forming separate molecules

the bonds extend throughout the entire solid like one giant molecule

THESE ARE THE STRONGEST COMPOUNDS!!!!
PROPERTIES OF NETWORK COVALENT BONDING:
http://youtu.be/PU9rzTjLyb4 (only watch until 4 min)
http://youtu.be/fsc7_JbxDuY - understand why these substances have the highest melting points and boiling points of any
substance on earth.
Ex:
10
BONDING
PRACTICE
Lewis Structure
Geometry
(shape)
Bond
Angle
Polarity of Bond
Use
electronegativity
chart
Polarity of Molecule
OCl2
C2Br2
SiCl4
AsCl3
CH3F
Si2Br4
SF2
CH2Cl2
11
Lewis Structure
Geometry
Bond
Angle
Polarity of Bond
Polarity of Molecule
SiH2Se
SO3-2
C2HBr
CBr4
SO4-2
12
VSEPR DIAGRAMS AND GEOMETRY
1. Complete the chart below.
SCRATCH WORK
STRUCTURAL,
LEWIS OR VSEPR
DIAGRAM
NAME OF
SHAPE
BOND
ANGLE
IS THE
MOLECULE
POLAR?
MP/BP?
DISSOLVES
IN?
(YES OR NO?)
(dispersion or dipole?)
Cl2
O2
HBr
CH2S
13
14
DIAGRAM
(scratch work)
STRUCTURAL,
LEWIS OR VSEPR
DIAGRAM
NAME OF
SHAPE
BOND
ANGLE
IS THE
MOLECULE
POLAR?
MP/BP
DISSOLVES
IN?
(YES OR NO?)
(dispersion or dipole?)
CF4
PH3
H2S
CS2
15
DIAGRAM
(scratch work)
STRUCTURAL,
LEWIS OR VSEPR
DIAGRAM
NAME OF
SHAPE
BOND
ANGLE
IS THE
MOLECULE
POLAR?
MP/BP
DISSOLVES
IN?
(YES OR NO?)
(dispersion or dipole?)
CF2Cl2
PF3
OH-1
CO3-2
16
COORDINATE COVALENT BONDING
Example: O3
PRACTICE WITH COORDINATE COVALENT EXAMPLES:
Formula
Lewis Structure
Molecular Shape
(diagram)
Name of
Shape
Bond
Angle
1. NO3-1
2. SO2
3. SO3-2
17
Work Space
NO3-1
Work Space
SO2
Work Space
Work Space
SO4-2
18
19
HOMEWORK #1: INTERMOLECULAR FORCES
1. Label the substances below as: metallic, ionic, network covalent, molecular (nonpolar (dispersion)),
molecular (polar (dipole)) or molecular (hydrogen bonding)
a. melts at 800°C, conducts electricity as a solid, does not dissolve in water
__________________
b. strong odor, dissolves in gasoline, melts easily when heated
__________________
c.
crystalline solid, dissolves in water, solution conducts electricity
__________________
d.
crystalline solid, does not dissolve in water or acetone, very high melting point _______________
e. K2SO4
__________________
f. CH4
__________________
g. H2O
__________________
2.
Fill in the missing boxes in the chart below. The types of solid used are: Molecular (nonpolar),
Molecular (polar); Ionic, Network Covalent, Metallic
Appearance
Time to Melt?
Dissolves in?
(water, alcohol,
acetone)
Conductivity?
1
crystalline
solid
> 10 minutes* water
(*would not
melt in our lab)
2
Shiny solid
> 10 minutes*
(*would not
melt in our lab)
4 minutes
3.
crystalline
solid
flaky solid
30 seconds
none
> 10 minutes* did not dissolve
(*would not
melt in our lab)
none
Crystalline
solid
Type?
As solid; liquid not
tested
water, alcohol
4.
5.
20
HOMEWORK #2: DRAWING LEWIS
1. Draw each molecule below with the correct bonding. Follow the steps below:
a. Position atoms as symmetrically as possible.
b. Count to make sure all atoms are up to 8 electrons, except hydrogen (2) or boron (6).
a. H2O
b. HOBr
c. H2CS
d. HCP
e. PH3
f. HCN
g. CS2
h. BF3
i. CCl4
2. Draw a Lewis dot diagram for each ionic compound below:
a. RbCl
b. AlF3
21
HOMEWORK #3: LEWIS DIAGRAMS
SCRATCH WORK
STRUCTURAL,
LEWIS OR VSEPR
DIAGRAM
NAME OF
SHAPE
BOND
ANGLE
IS THE
MOLECULE
POLAR?
(YES OR NO?)
(dispersion or dipole?)
H2Se
AsF3
BF3
**B is an
exception,
it only gets
6
N2
SiCl4
2. Complete the chart below:
Formula
Lewis Structure
Molecular Shape
(diagram)
Name of
Shape
Bond
Angle
Polar?
Dipole or
Dispersion?
1. PBr3
22
MP/
2. C2Cl2
3. SiCl4
4. O2
5. PO43-
23