COVALENT BONDING
Unit 6
COVALENT BOND:
 Atoms
that are held together by sharing
electrons
Usually 2 non-metals
 Forms a molecule (or molecular compound)
 Tend to have low melting and boiling points
 Described by a molecular formula

REVIEW

What is electronegativity?
 How
attracted are electrons to the atom
 (how
“likely” is the atom to become more negative by
gaining an electron)
OCTET RULE
 Atoms
tend to form bonds to acquire a
total of 8 electrons



Single bond
=
1 pair of e-
Double bond
Triple bond
=
=
2 pairs of e3 pairs of e-
 Electron
dot structures are used to
represent the shared pair of
electrons
STRUCTURAL FORMULAS:
• Each dash indicates a pair of shared e
Single Bond
H• + •H
• Double Bond
••
••
•• O • + •O••
•
•
• Triple Bond
•
•
•• N • + •N••
•
•
H •• H
H
H
O
O
O O
N
N
N N
EXAMPLES:
Water, H2O
EXAMPLES:
Ammonia, NH3
EXAMPLES:
Methane, CH4
EXAMPLES:
Propane, C3H8
EXAMPLES:
Propene, C3H6
EXAMPLES:
Propyne, C3H4
LEWIS (ELECTRON) STRUCTURE




Step 1
 count total valence e involved
Step 2
 connect the central atom (usually the first in the
formula) to the others with single bonds
Step 3
 complete valence shells of outer atoms
Step 4
 add any extra e to central atom
IF the central atom has 8 valence e- surrounding it . . YOU’RE
DONE!
Given below is an outline of how to determine the "best" Lewis
structure for NO3-.
1. Determine the total number of valence electrons in a molecule
N (1) = 5
O (3) = 18
1 neg charge = 1
2. Draw a skeleton for the molecule which connects all atoms using
only single bonds. In simple molecules, the atom with the most
available sites for bonding is usually placed central.
3. Of the 24 valence electrons in NO3-, 6 were required to make the
skeleton. Consider the remaining 18 electrons and place them so as to
fill the octets of as many atoms as possible (start with the most
electronegative atoms first then proceed to the more electropositive
atoms).
4. Are the octets of all the atoms filled? If not then fill the
remaining octets by making multiple bonds (make a lone pair of
electrons, located on a more electronegative atom, into a bonding pair
of electrons that is shared with the atom that is electron deficient).
SOMETIMES…
You only have two atoms, so there is no central
atom, but follow the same rules.
 Check & Share to make sure all the atoms are
“happy”.

Cl2
Br2
H2
O2
N2
HCl
PRACTICE
1) CO2
2) SiO2
3) PCl3
4) NO2-1
5) CH3F
PRACTICE
1) CO2
2) SiO2
3) PCl3
4) NO2-1
5) CH3F
Resonance structures:
• Occur when it is possible to write 2 or more
structural formulas for a compound
• Ex: NO3-
DIATOMIC
You must memorize these!!
H2
N2
O2
F2 Cl2
Br2
Magnificent 7—
I2
NAMING COVALENT COMPOUNDS

Similar to ionic bonding

CO

CO2
NAMING
We need to say how many of each element we have!
Use the prefixes!
1- mono
2- di
3- tri
4- tetra
5- penta
Examples: NO
SiCl4
6- hexa
7- hepta
8- octa
9- nona
10- deca
NAMING

First Element: If you have more than one of the
first element then you use a prefix. If there is
only one then you just state the element

Second Element: Always has a prefix
PRACTICE

1.
2.
3.
4.
5.
Formulas to names
SO3
ICl3
PBr5
CO
CO2

Names to formulas
1. Carbon tetrachloride
2. Dinitrogen monoxide
3. Dinitrogen tetroxide
4. Phosphorus triiodide
5. Sulfur heptafluoride
ACIDS TO MEMORIZE
Hydrochloric- HCl
Acetic Acid- HC2H3O2
Nitric Acid- HNO3
Sulfuric Acid- H2SO4
Carbonic Acid- H2CO3
Phosphoric Acid- H3PO4
TYPES OF COVALENT
BONDS
NON-Polar bonds
Electrons
shared evenly in the bond
E-neg difference is zero
Between identical atoms
Diatomic molecules
TYPES OF COVALENT
BONDS
Polar bond
Electrons
unevenly shared
E-neg difference greater than zero
but
less than 2.0
closer to 2.0 more polar
more “ionic character”
PLACE THESE MOLECULES IN ORDER OF INCREASING BOND
POLARITY
WHICH IS LEAST AND WHICH IS MOST?
 HCl
 CH4
 CO2
 NH3
 N2
 HF
a.k.a.
“ionic character”
NON-POLAR MOLECULES
 Sometimes
the bonds within a
molecule are polar and yet the
molecule is non-polar because its
shape is symmetrical.
H
Draw Lewis dot first and
see if equal on all sides
H C H
H
POLAR MOLECULES (A.K.A.
 Not
DIPOLES)
equal on all sides
Polar
bond between 2 atoms
makes a polar molecule
asymmetrical shape of molecule
+
H Cl

SPACE FILLING MODEL
“ELECTRON-CLOUD” MODEL
+

H
Cl
