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.
CO
2
C
6
H
12
O
6
Molecules and Molecular Compounds Molecule- smallest electrically neutral unit, still has properties of the substance Made from only nonmetals Can be from one element- O
2
Can make a compound- CO
2
Chemical Formulas More than one atom? –use a subscript (H 2 O) There are 7 diatomic elements Hydrogen (H
2
), Nitrogen (N
2
), Oxygen (O
2
), Fluorine (F
2
), Chlorine (Cl
2
), Bromine (Br
2
), and Iodine (I
2
) Remember: “Br I N Cl H O F”
Molecules and Molecular Compounds
CO
2
C O O
Molecules and Molecular Compounds
O
2
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 –O
2
, O
3
, H
2
O
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
H
H one pair of electrons.
H H
Shared electrons.
One pair of electrons.
H
H
H H
Single Covalent Bonds
F F F F
Shared electrons.
One pair of electrons.
F
2s Single Covalent Bonds
F F
2p 2s
F
2p
Single Covalent Bonds H
O O H H H
O H O
2s H Single Covalent Bonds 2p
H
1s
H
1s
Double Covalent Bonds Atoms held together by sharing O
O O
Shared electrons.
2 Pairs of electrons.
Double Covalent Bonds O
O C
2p 2s
O O
2s 2p
Double Covalent Bonds O
O C
O
O C
Triple Covalent Bonds Atoms held together by sharing three pairs of electrons.
N N
N N
Shared electrons.
3 Pairs of electrons.
Triple Covalent Bonds N
N
2p 2s
N N
2s 2p
Coordinate Covalent Bonds O
C
O
C
Carbon Monoxide
Coordinate Covalent Bonds O
C
Takes place when the shared electron pair comes from one of the bonding atoms.
C
O Coordinate Covalent Bonds 2p 2s
O C
2s 2p
Coordinate Covalent Bonds
H N H H
Ammonia NH 3
Coordinate Covalent Bonds
H H
+
N H H
Ammonium NH 4
Bond Dissociation Energy The energy needed to break the bond between two covalently bonded atoms.
H
H O O
Energy
Resonance
O
O
O O O
O Ozone
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.
NO 2 Nitrogen Dioxide O
O N
N O
O
NO 2 Nitrogen Dioxide
O
2s 2p 1 2
N
3 4 5
O
2s 6 7 2p
8 8
PCl 5
Cl Cl
10 8
Cl Cl Cl
8
Phosphorus Pentachloride
8
Homework Section 8-2 Practice Problems Review Due: 12/02/05
7a 7b
Cl Cl
7c
Br Br I I
8a
H O O
H
8b
Cl P Cl Cl
9a [
H O
] -
10
F F B F F
11
O O S
O O 2-
12
H O C
O
O
21
H S H H P H H Cl F
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 orbital
+
+
p
atomic 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
CO
2 Linear
O C O
BCl
3 Trigonal Planar
Cl B Cl
120 °
Cl
CH
4 Tetrahedral
H H C H H
NH
3 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
F F O
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
Cl
H
+ 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
O H
H
O H +
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