Covalent Bonding
Covalent Bonding
• Electrons are shared
between two nonmetals
• Weaker attractive force
than ionic bonding
Properties of Molecular
Compounds
State at SATP
Structure
Typically gases & liquids,
but some solids
Variable (waxy to brittle)
Melting & Boiling Points Low
Electrical Conductivity
Nonelectrolyte
Solubility in Water
Variable (low to high)
Covalent Bonding
Lone pairs, valence electrons
not involved in covalent bond
• Formation of hydrogen chloride:
H Cl






Cl

H +


 H - Cl



Covalent bond, shared electrons
Structural Formula: H-Cl
(lone pairs are not drawn)
Polyatomic Ions
• Many compounds contain a combination of
covalent and ionic bonds.
• E.g. NaOH
• OH- is a polyatomic ion with a covalent
bond between O and H
• Ionic bond between Na+ and OH-
Lewis Structures
H  +  H  H H or H H




Cl
Cl
 
Structural Formula: Cl-Cl

or

Cl
Cl






Cl
+
Cl



Cl2:




H2:
Double and Triple Bonds
• Atoms can share 4 electrons to form a double bond
or 6 electrons to form a triple bond.


N 2:
N N

O
=O



O 2:
• The number of shared electron pairs (covalent
bonds) that an atom can form is the
bonding capacity.
Coordinate Covalent Bonds
A covalent bond in which both of the shared electrons come
from the same atom.
e.g. NH3 (ammonia) and H+ (hydrogen ion) to form NH4
(ammonium)
Drawing Lewis Structures
1. Arrange the element symbols.
•
Central atoms are generally those with the highest bonding capacity.
•
Carbon atoms are always central atoms
•
Hydrogen atoms and halogen atoms are always peripheral atoms
2. Add up the number of valence electrons from all atoms.
•
For polyatomic ions, add one electron for each negative charge and
subtract one for each positive charge.
3. Draw a skeleton structure with atoms attached by single
bonds.
4. Complete the octets of peripheral atoms.
5. Place extra electrons on the central atom.
6. If the central atom doesn’t have an octet, try forming
multiple bonds by moving lone pairs.
SAMPLE PROBLEM
PROBLEM:
Writing Lewis Structures for Molecules with
One Central Atom
Write a Lewis structure for CCl2F2, one of the compounds
responsible for the depletion of stratospheric ozone.
Draw Lewis structures for:
CH4



H N H

H
H

H C
H

H

or
or
or
or



H O
H


NH3


H 2O
H 
F

HF


H F


H O
H


H N H
H
H
H C H
H
SAMPLE PROBLEM
PROBLEM:
Writing Lewis Structure for Molecules with
More than One Central Atom
Write the Lewis structure for methanol (molecular formula
CH4O), an important industrial alcohol that is being used as a
gasoline alternative in car engines.
SAMPLE PROBLEM
PROBLEM:
Writing Lewis Structures for Molecules with
Multiple Bonds.
Write Lewis structures for the following:
(a) Ethylene (C2H4), the most important reactant in the
manufacture of polymers
(b) Nitrogen (N2), the most abundant atmospheric gas
Drawing Lewis Structures –
more practice 


14 e-


H O
Cl





O
26 e-



ClO3


HOCl
24 e-
O
Cl
O




COCl2


O


Cl
C
Cl


Practice Problems
• p.79 #2
• p. 80 #3
• p. 81 #5, 6, 9,13 - 15