Transcript Chapter 8 Notes - Hingham Schools

Chapter 8
Covalent Bonding
Hingham High School
Mr. Dan Clune
Chemical Formulas
Shows the kind and number of
atoms in the smallest piece of
a substance.
Molecular formula- number
and kinds of atoms in a
molecule.
CO2
CH O
Molecules and Molecular
Compounds
Molecule- smallest electrically
neutral unit, still has properties
of the substance
Made from only nonmetals
Can be from one element- O2
Can make a compound- CO2
Chemical Formulas
More than one atom? –use a
subscript (H2O)
There are 7 diatomic elements
Hydrogen (H2), Nitrogen (N2),
Oxygen (O2), Fluorine (F2),
Chlorine (Cl2), Bromine (Br2), and
Iodine (I2)
Remember: “Br I N Cl H O F”
Molecules and Molecular
Compounds
CO2
C
O
O
Molecules and Molecular
Compounds
O2
O
O
Diatomic
Molecules and Molecular
Compounds
Properties of molecular
compounds
–Low melting and boiling points
–Usually gas or liquid
–Composed of two or more
nonmetals
–O2, O3, H2O
Covalent Bonds
Nonmetals join or bond by sharing
electrons.
O
O
Shared electrons.
Homework
Section 8-1
Practice Problems
Review
Due: 12/01/05
Covalent Bonds
Nonmetals join or bond by sharing
electrons.
O
O C
Shared electrons.
Octet Rule
Covalent Bonding
In forming covalent bonds,
electron sharing tends to occur
so that atoms, with shared
electrons included, attain the
configuration of noble gases.
Single Covalent Bonds
Atoms held together by sharing
one pair of electrons.
H
H
Shared electrons.
H H
One pair of
electrons.
H
H
H H
1s
Single Covalent Bonds
F F
Shared electrons.
F F
One pair of
electrons.
Single Covalent Bonds
F F
2p
F
2s
2p
2s
F
Single Covalent Bonds
H
O
H
O H
H
H
O
H
O
Single Covalent Bonds
H
1s
2s
2p
1s
H
Double Covalent Bonds
Atoms held together by sharing
two pairs of electrons.
O
Shared electrons.
O
O
O
2 Pairs of
electrons.
Double Covalent Bonds
2p
O
2s
2p
O
O C
2s
O
Double Covalent Bonds
O C
O
O C
O
Triple Covalent Bonds
Atoms held together by sharing
three pairs of electrons.
N
Shared electrons.
N
N
N
3 Pairs of
electrons.
Triple Covalent Bonds
N
N
2p
N
2s
2p
2s
N
Coordinate Covalent Bonds
O
O
C
C
Carbon Monoxide
Coordinate Covalent Bonds
O
C
Takes place when the shared
electron pair comes from one
of the bonding atoms.
O
C
Coordinate Covalent
Bonds
2p
C
2s
2p
2s
O
Coordinate Covalent Bonds
H
N H
H
Ammonia NH3
Coordinate Covalent Bonds
H
+
H N H
H
Ammonium NH4
Bond Dissociation Energy
The energy needed to break the
bond between two covalently
bonded atoms.
Energy
H
H OO
Resonance
O O O
Ozone
O
O
O
A resonance structure is a
structure that occurs when it
is possible to write two or
more valid electron dot
formulas that have the same
number of electron pairs for a
molecule or ion.
Octet Rule Exceptions
The Octet Rule cannot be
satisfied in molecules whose
total number of valence
electrons is an odd number.
There are also molecules in
which an atom has fewer, or
more , than a complete octet of
valence electrons.
NO2 Nitrogen Dioxide
O N O
O N O
NO2 Nitrogen Dioxide
O
N
O
2s
2p
1
2
3 4
5
6 7
2s
2p
8
8
Cl
Cl
Cl 10
P
Cl
Cl
8
8
8
PCl5 Phosphorus Pentachloride
Homework
Section 8-2
Practice Problems
Review
Due: 12/02/05
7a
7b
Br Br
Cl Cl
7c
I
I
8a
H
H OO
8b
Cl
P
Cl
Cl
9a
[
H
O]
10
F
F B F
F
11
O
O
O S
2-
O
12
O
H OC
O
21
H SH
H P H Cl F
H
23
O
S
O
O S O
Bonding
Theories
Molecular Orbitals
Just as an atomic orbital
belongs to a particular atom, a
molecular orbital belongs to a
molecule as a whole.
Sigma Bonds
When two atomic orbitals
combine to form a molecular
orbital that is symmetric
around the axis connecting
two atomic nuclei.
σ Bonds
σ Bonds
+ + +
s atomic
orbital
+ +
Sigma Bonding
Molecular
Orbital
σ Bonds
+
+
+
p atomic
p atomic
orbital
orbital
σ Bonds
Sigma Bonding Molecular
Orbital
π (Pi) Bonds
+
+
+
π (Pi) Bonds
VSEPR Theory
The repulsion between
electron pairs causes
molecular shapes to adjust
so that valence-electron
pairs are as far apart as
possible.
Molecular
Models
Linear
CO2
O C O
Trigonal Planar
BCl3
Cl
B
Cl 120°Cl
CH4
Tetrahedral
H
H C H
H
NH3
Pyramidal
H N H
H
107°
Hybrid Orbitals
Orbital Hybridization provides
information about both
molecular bonding and
molecular shape.
In hybridization,
several atomic
orbitals mix.
Homework
Section 8-3
Review
Practice Problems
Due: 12/05/05
Polar Bonds
and
Polar Molecules
Non-Polar Bonds/Molecule
Non-Polar Bonds and Molecules
occur when the electrons are
shared equally between
atoms.
O
O
F F
Polar Covalent Bonds
The more electronegative atoms
attract electrons more strongly
and gains a slightly negative
charge, the less
electronegative atom,
slightly positive.
Polar Covalent Bonds
-
H
- +
Cl
O
+
H
H
Polar Molecule
In a Polar Molecule one end
of the molecule is slightly
negative and the other end
is slightly positive.
Non-Polar Molecule
- + -
O C O
Positive in the middle and
negatives at each end cancel
out.
Attraction Between Molecules
Inter-Molecular attraction
between molecules is less than
ionic or covalent bonds.
Hydrogen Bonding
H
H
O
H
-
O
+
H
Hydrogen Bonding
Hydrogen Bonds are attractive
forces in which a hydrogen
covalently bonded to a very
electronegative atom is weakly
bonded to an unshared electron
pair of another electronegative
atom.
Van der Waals Forces
Dipole Interaction – electrical
attraction between molecules
(similar to ionic bonds).
Dispersion Forces – caused
by moving electrons, electrons
are located more on one side
of the atom.
Intermolecular Attractions
and
Molecular Attractions
Lower melting points than
ionic bonds.
Usually liquids and gasses.
Some solids. (network solids.)
Network Solids
Molecules covalently
bonded to other molecules.
Very strong bonds.
Diamond
Network Solids
Homework
Section 8-4
Review
Practice Problems
Due: 12/06/05