Transcript No Slide Title

Chemical Bonding
Ionic and Covalent
Bond
.
Valence electrons are the outer shell electrons
of an atom. The valence electrons are the
electrons that particpate in chemical bonding.
Kernal is the rest of the atom
Group
1A
3A
e- configuration # of valence ens1
1
ns2np1
3
5A
ns2np3
5
7A
ns2np5
7
9.1
9.1
A covalent bond is a chemical bond in which
two or more electrons are shared by two
atoms. Covalent bonds are exothermic.
F + F
7e7e-
FF
8e-8e-
Lewis structure of F2
lone pairs
single covalent bond
one pairs
FF
F
F
lone pairs
single covalent bond
lone pairs
9.4
Lewis structure of water
single covalent bonds
H + O + H
H O H or H O H
- 2e
- 2e8e
Double bond – two atoms share two pairs
of electrons
or
O C O
O
O
C
-8edouble bonds
8e-8ebonds
double
Triple bond – two atoms share three
pairs of electrons
or
N N
N N
-bond
triple
8e8e
triple bond
9.4
Polar covalent bond or polar bond is a
covalent bond with greater electron density
around one of the two atoms
electron poor electron rich
region
region
F
H
e- poor e- rich
H F
d+ d-
9.5
Electronegativity
• A polar bond is a covalent bond in
which the bonding electrons are not
shared equally by the two atoms.
• Electronegativity is a measure of the
ability of an atom to attract the
shared e- in a chemical bond.
• Polarity is the degree of charge
separation of the bond.
The Ionic Bond
The bond that results from the
electrostatic attraction between
positively charged cations and
negatively charged anions. Ionic bonds
are exothermic.
Li + F
Li+ F -
222p6
21s
1s21s
2s212s22p
1s5[He]
2s
[Ne]
9.2
9.5
Classification by difference in electronegativity
% ionic character Bond Type
0-5
Nonpolar Covalent
 50
Ionic
5 > and ≤50
Polar Covalent
% ionic character =Highest –lowest/highest x 100
Increasing difference in electronegativity
Non polar Covalent Polar Covalent
share e-
partial transfer
of e-
Ionic
transfer e-
9.5
Classify the following bonds as ionic, polar
covalent, or covalent: The bond in CsCl; the
bond in H2S; and the NN bond in H2NNH2.
Cs – 0.7 Cl – 3.0
H – 2.1
S – 2.5
N – 3.0
N – 3.0
Ionic
Polar Covalent
Covalent
9.5
Writing Lewis Structures
1. Draw skeletal structure of compound
showing what atoms are bonded to each
other. Put least electronegative element in
the center. Hydrogen cannot be in the center
2. Count total number of valence e-. Add 1 for
each negative charge. Subtract 1 for each
positive charge.
3. Complete an octet for all atoms except
hydrogen
4. If structure contains too many electrons,
form double and triple bonds.
9.6
Write the Lewis structure of nitrogen trifluoride
Step 1 – N is less electronegative than F,
put N in center
Step 2 –count valence electrons N - 5 and F - 7
5 + (3 x 7) = 26 valence electrons
Step 3 – Draw single bonds between N and F
atoms and complete octets on N and F atoms.
Step 4 - Check, are # of e- in structure equal to
number of valence e- ?
F N F
3 single bonds (3x2)
+
10
lone
pairs
(10x2)
=
F
26 valence electrons
9.6
Write the Lewis structure of the carbonate ion
Step 1 – C is less electronegative than O,
put C in center
Step 2 – Count valence electrons C - 4 and O-6
-2 charge – 2e4 + (3 x 6) + 2 = 24 valence electrons
Step 3 – Draw single bonds between C and O
atoms and complete octet on C and O atoms.
Step 4 - Check # of e- in structure
3 single bonds (3x2) + 10 lone pairs (10x2) =
26 valence electrons
O C O Step 5 - Too many electrons,
form double bond and
O
re-check # of e9.6
The enthalpy change required to break a
particular bond in one mole of gaseous
molecules is the bond energy.
Bond Energy
H2 (g)
H (g)+ H (g) DH0 = 104 kcal
HCl (g)
O2 (g)
N2 (g)
H (g)+ Cl (g)DH0 = 103 kcal
O (g)+ O (g)DH0 = 119 kcal O O
N (g)+ N (g) DH0 = 226 kcal N N
Bond Energies
Single bond < Double bond < Triple bond
9.10
Average bond energy in polyatomic
molecules
OH
H + O DH0 = 111 kcal
9.10
Using the bond energies from pg
131 in the chemistry books, what
is the bond energies for the
following compounds?
CH4
CCl4
HBr
H2O
N2
O2
Oxidation numbers match the
charge of an item.
Examples:
Cl 0
Na+1 1
O-2 -2
F 0
LEO goes GER
Lose electron it is oxidation
Gain electron it is reduction