Transcript Covalent Bonding

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)
Confused?? Don’t worry…more answers to come
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)
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.
Multiple Covalent Bonds
•
•
••
••
N N
•
•
•
N N
••
••
•
N N
••
•
••
•N
•
N•
••
•
••
•
Multiple Covalent Bonds
•O
••
••
•
•
•
••
•
••
••
O C O
•
•
•
••
•
••
O C O
••
• C•
•
••
••
O•
•
••
••
••
••
O C O
••
•
••
•
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 are always peripheral atoms
2. Add up the number of valence electrons from all atoms.
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.
Practice Problems
• Examples
– Methanal CH2O
– Chlorate (polyatomic ion)
• p.77-81 #1-15
Strategy for
Writing Lewis
Structures
Draw Lewis structures and the structural formula for:
CH4:



H N H

H
H

H C
H

H

or
or
or
or



H O
H


NH3:


H2O:
H 
F

HF:


H F


H O
H


H N H
H
H
H C H
H
Sum of
valence e-
:
: F:
: F:
:
Atom
placement
For NF3
:
Molecular
formula
N
Remaining
valence eLewis
structure
:
: F:
Zero: NF3 is uncharged
N = 5eF = 7eTotal
X 3 = 21e26e-
SAMPLE PROBLEM 10.1
Write a Lewis structure for CCl2F2, one of the compounds
responsible for the depletion of stratospheric ozone.
SOLUTION:
:
:
: Cl :
:Cl C
: F:
:
Make bonds and fill in remaining valence
electrons placing 8e- around each atom.
F
F
:
Steps 2-4:
C has 4 valence e-, Cl and F each have 7. The
sum is 4 + 4(7) = 32 valence e-.
Cl C
:
Step 1: Carbon has the highest bonding capacity and is
the central atom.
The other atoms are placed around it.
Cl
F:
:
PROBLEM:
Writing Lewis Structures for Molecules with
One Central Atom
SAMPLE PROBLEM 10.2
Hydrogen can have only one bond so C and O must be next
to each other with H filling in the bonds.
There are 4(1) + 4 + 6 = 14 valence e-.
C has 4 bonds and O has 2. O has 2 pair of nonbonding e-.
H
:
SOLUTION:
Write the Lewis structure for methanol (molecular formula
CH4O), an important industrial alcohol that is being used as a
gasoline alternative in car engines.
H
C
O
:
PROBLEM:
Writing Lewis Structure for Molecules with
More than One Central Atom
H
H
SAMPLE PROBLEM 10.3
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
PROBLEM:
PLAN:
For molecules with multiple bonds, there is a Step 5 which follows the
other steps in Lewis structure construction. If a central atom does not
have 8e-, an octet, then e- can be moved in to form a multiple bond.
(a) There are 2(4) + 4(1) = 12 valence e-. H can have only
one bond per atom.
SOLUTION:
H
H
:
H
C
C
H
H
H
H
C
C
H
(b) N2 has 2(5) = 10 valence e-. Therefore a triple bond is required to make
the octet around each N.
N
.
:
N
.
:
:
:.
N
.
N
N
:
.:
N
.
Drawing Lewis Structures

CH3OH
14 ve’s
14 ve’s



H O
Cl



HOCl
24 ve’s

COCl2


O


Cl
C
Cl


H

H C O
H

H