CHAPTER 12 CHEMICAL BONDING

1
CHAPTER 12 CHEMICAL BONDING
CHEMICAL BOND A force that holds two or more
atoms together as a unit Individual atoms will
naturally bond together to achieve a lower energy
state (to be more stable)
3B-1 (of 42)
2
TYPES OF BONDS
1) METAL ATOMS AND NONMETAL ATOMS
Metal atoms easily lose electrons forming
positive ions, and nonmetal atoms easily gain
electrons forming negative ions
IONIC BOND The electrostatic attraction between
positive and negative ions Ionic bonding forms
giant crystalline networks containing billions of
positive and negative ions that are strongly
attracted together Ionic bonding exists between
metal and nonmetal ions
3B-2
3
Elemental Iron
Elemental Oxygen
Rust

Fe atoms
O atoms (molecules)
Fe ions and O ions
3B-3
4
2) NONMETAL ATOMS
Nonmetal atoms attract each others valence
electrons, and share the valence electrons
between pairs of atoms Covalent Bond The
electrostatic attraction of shared electrons to
the nuclei of bonding nonmetal atoms Covalent
bonding forms individual units called molecules,
and while the atoms that covalently bond together
strongly attract each other, the molecules that
are created weakly attracted each other Covalent
bonding exists between nonmetal atoms
3B-4
5
Elemental Chlorine
Elemental Carbon
Carbon Tetrachloride

C atoms
Cl atoms (molecules)
CCl4 molecules
3B-5
6
Picture
NONPOLAR COVALENT BOND A bond in which 2 atoms
are sharing electrons equally POLAR COVALENT BOND
A bond in which 2 atoms are sharing electrons
unequally IONIC BOND A bond in which two atoms
have transferred electrons
3B-6
7
ELECTRONEGATIVITY The attraction of an atom for
shared electrons
Atom with the highest EN?
Atom with the lowest EN?
The difference in the ENs of 2 atoms tells the
type of bond they make
EN Difference Bond
0.0 0.1 to 1.6 1.7 to 3.3
Nonpolar Covalent Polar Covalent Ionic
3B-7
8
N-N Bond EN for N 3.0 3.0 3.0 0.0 ?
Nonpolar Covalent Bond
3B-8
9
C-O Bond EN for C 2.5, O 3.5 3.5 2.5
1.0 ? Polar Covalent Bond
H-S Bond EN for H 2.1, S 2.5 2.5 2.1
0.4 ? Polar Covalent Bond
Polar covalent bonds have partially positive and
a partially negative ends
C O d d-
H S d d-
C O
H S
DIPOLE MOMENT The amount of separation of the
positive and negative charges in a bond
DIPOLE MOMENT ARROW Shows the direction of the
dipole moment, pointing toward the negative end
of the bond
3B-9
10
Na-Cl Bond EN for Na 0.9, Cl 3.0 3.0 0.9
2.1 ? Ionic Bond
Na Cl-
3B-10
11
BONDING IN IONIC COMPOUNDS Atoms form ions to
obtain a stable, octet electron arrangement
Sodium chloride
. . . Cl . .
Na
-

A sodium chloride crystal is a symmetrical array
of sodium and chloride ions in a 11
ratio EMPIRICAL FORMULA The simplest whole
number ratio of atoms of different elements in a
compound Empirical Formula NaCl
3B-11
12
Magnesium fluoride
. . . F . .
. . . F . .

-
2
-
Mg
Empirical Formula MgF2
3B-12
13
Potassium nitride
Empirical Formula
3B-13
14
SIZES OF ATOMS AND IONS
Positive ions are smaller than their neutral
atoms and negative ions are bigger than their
neutral atoms
Na atom
Cl atom
Na ion
Cl- ion
3B-14
15
Sizes of atoms or ions are determined by
1) The more energy levels an atom or ion has the
larger it will be 2) With the same number of
energy levels, the more protons an atom or ion
has the smaller it will be
Li F Na Cl
Li F- Na Cl-
Electrons Energy Levels Protons Big to Small
3 2 3 3rd
9 2 9 4th
11 3 11 1st
17 3 17 2nd
2 1 4th
10 2 9 2nd
10 2 11 3rd
18 3 1st
ISOELECTRONIC Ions or atoms with the same
number of electrons
3B-15
16
BONDING IN COVALENT MOLECULES Atoms share
electrons to obtain a stable, octet (or duet)
arrangements
Water (H2O)
. . . O .
H
H
. . H O H
? LONE PAIR
? BONDING PAIR
LEWIS STRUCTURE A diagram using electron dot
notation to show how the valence electrons are
arranged among bonded atoms
3B-16
17
To draw a proper Lewis Structure
1 Add up the valence e-s for all of the atoms
in the molecule or ion
2 Draw a skeletal structure by using pairs of
electrons to make bonds
3 Complete octets (or duets for H) for all
atoms, outer atoms first, using the remaining
valence e-s
4 If octets are not produced, make the atoms
that have octets share more e- pairs with atoms
that do not have octets
3B-17
18
Sulfur dichloride, SCl2
6 7 7 20 valence e-s
Cl S Cl
3B-18
19
Phosphorus tribromide, PBr3
3B-19
20
Ammonia, NH3
5 1 1 1 8 valence e-s
H N H H
3B-20
21
Methane, CH4
3B-21
22
Fluorine, F2
7 7 14 valence e-s
F F
SINGLE BOND One shared pair of e-s between two
atoms
3B-22
23
Oxygen, O2
6 6 12 valence e-s
O O
DOUBLE BOND Two shared pairs of e-s between two
atoms
3B-23
24
Nitrogen, N2
5 5 10 valence e-s
N N
TRIPLE BOND Three shared pairs of e-s between
two atoms
3B-24
25
Hydrogen cyanide, HCN
Carbon disulfide, CS2
1 4 5 10 valence e-s
H C N
3B-25
26
Sulfate, SO42-
Ammonium, NH4
6 4(6)
2 32 valence e-s
5 4(1)
- 1 8 valence e-s
2-
O O S O O
H H N H H

3B-26
27
Ozone, O3
6 6 6 18 valence e-s
or
O O O
O O O
O O O
O O O
?
RESONANCE When more than one Lewis structure
can be drawn for a molecule or ion RESONANCE
STRUCTURES The Lewis structures that can be
drawn for the molecule or ion The real ozone
molecule is a average of its resonance structures
3B-27
28
O O O
O O O
?
O O O
2 1½ bonds
3B-28
29
MOLECULAR SHAPE
VSEPR THEORY (Valence Shell Electron Pair
Repulsion) All atoms and lone pairs attached to
a central atom will spread out as far as possible
to minimize repulsion A Lewis structure must be
drawn to use the VSEPR Theory
3B-29
30
H H C H H
STERIC NUMBER (SN) The sum of the bonded atoms
and lone pairs on a central atom The steric
number of carbon is 4 (SN 4) 4 bonded atoms
and no lone pairs
Tetrahedral Bond angle is 109.5
3B-30
31
The steric number of nitrogen is 4 (SN 4) 3
bonded atoms and 1 lone pairs
H N H H
Trigonal Pyramidal Bond angle is 108
3B-31
32
. . H O H
The steric number of oxygen is 4 (SN 4) 2
bonded atoms and 2 lone pairs
Bent Bond angle is 105
3B-32
33
Formaldehyde, H2CO
1 1 4 6
12 valence e-s
H H C O
The steric number of carbon is 3 (SN 3) 2
bonded atoms and 1 lone pairs
Trigonal Planar Bond angle is 120
3B-33
34
SiS2
4 6 6
16 valence e-s
S Si S
The steric number of silicon is 2 (SN 2) 2
bonded atoms and 0 lone pairs
Linear Bond angle is 180
3B-34
35
SN 4 4 4 3 3 2
Atoms 4 3 2 3 2 2
Shape Tetrahedral Trigonal Pyramidal Bent
(109.5) Trigonal Planar Bent (120) Linear
Lone Pairs 0 1 2 0 1 0
3B-35
36
MOLECULAR POLARITY A BOND is polar if it has a
positive end and a negative end A MOLECULE is
polar if it has a positive end and a negative end

• To determine if a molecule is polar or nonpolar
• 1) Draw the correct Lewis structure
• Draw its correct shape
• Use ENs to determine if the BONDS in the
  molecule are polar or nonpolar
• For the polar bonds, label the positive and
  negative ends with d and d-
• If a line can be drawn separating all ds from
  all d-s, the molecule is polar, it not its
  nonpolar

3B-36
37
. . H O H
ENs O 3.5, H 2.1 3.5 2.1 1.4 ? the O-H
BONDS are polar All of the ds can be separated
from all of the d-s, ? the H2O MOLECULE is polar
d-
d-
d
d
3B-37
38
H N H H
ENs N 3.0, H 2.1 3.0 2.1 0.9 ? the N-H
BONDS are polar All of the ds can be separated
from all of the d-s, ? the NH3 MOLECULE is polar
d-
d-
d-
N
H
H
d
d
H
d
3B-38
39
Carbon tetrafluoride, CF4
4 4(7)
32 valence e-s
F F C F F
d-
ENs C 2.5, F 4.0 4.0 2.5 1.5 ? the C-F
BONDS are polar All of the ds cannot be
separated from all of the d-s, ? the CF4
MOLECULE is nonpolar
d
d
d
d-
d-
d
d-
3B-39
40
REVIEW FOR TEST
Electromagnetic Radiation, Photons Ground State,
Excited State Orbital Energy Levels Sublevels Orbi
tal Notation Electron Configuration
Notation Electron Dot Notation Valence
Electrons Octet Electron Pair
2B-40
41
REVIEW FOR TEST
Periodic Trends in Metal, Nonmetal
Activity Atomic Radii Ionization
Energy Electron Affinity Ionic Bonds, Covalent
Bonds Electronegativity Bond Polarity from
Electronegativities Ion Sizes
2B-41
42
REVIEW FOR TEST
Lewis Structures for Ionic Compounds Covalent
Compounds Resonance Molecular Shapes Molecular
Polarity
2B-42