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Chapter 6 Section 2 Covalent Bonding... pages 178-189
1
Modern ChemistryChapter 6
Chemical Bonding
Sections 1-5Introduction to Chemical Bonding
Covalent Bonding & Molecular CompoundsIonic Bonding & Ionic Compounds
Metallic BondingMolecular Geometry
Chapter 6 Section 2 Covalent Bonding... pages 178-189
2
Chapte
r V
oca
bula
ryMoleculeMolecular
compoundChemical formulaMolecular formulaBond energyElectron-dot
notationLewis StructureStructural formulaSingle bondMultiple bondResonance
Chapter 6 Section 2 Covalent Bonding... pages 178-189
3
Section 2
Covalent Bonding and
Molecular Compounds
Chapter 6 Section 2 Covalent Bonding... pages 178-189
4
Molecules• A neutral group of atoms that are
held together by covalent bonds• Has all the physical and chemical
properties of the compound• May consist of two or more atoms
of the same element Diatomic elements I2 Br2 Cl2 F2 O2 N2
H2
Molecular elements S8 P4
I Bring Clay For Our New House & Swimming Pool.
Chapter 6 Section 2 Covalent Bonding... pages 178-189
5
Formulas• Chemical Formula – indicates
the relative numbers of atoms of each kind in a chemical compound by using symbols and numeric subscripts
• Molecular Formula – shows the types and number of atoms in a single molecule
Chapter 6 Section 2 Covalent Bonding... pages 178-189
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Formation of a Covalent Bond• Forces to consider
– Electrons repel each other– Protons and electrons attract each
other– e- to p+ attraction is greater than
the e- to e- repulsion
Chapter 6 Section 2 Covalent Bonding... pages 178-189
9
Formation of a Covalent Bond• Potential Energy and Stability
– High P.E. is related to low stability– Low P.E. is related to high stability
Chapter 6 Section 2 Covalent Bonding... pages 178-189
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Characteristics of Covalent Bonds• Bond Length – the distance between
two bonded atoms at their minimum potential energy
• Energy is released when a bond forms
• The same amount of energy is required to break that bond
• Bond Energy – the energy required to break a chemical bond and form neutral atoms.
Chapter 6 Section 2 Covalent Bonding... pages 178-189
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Octet Rule• Chemical compounds tend to form
so that each atom by gaining, losing or sharing electrons has an octet of electrons in its highest energy level
Chapter 6 Section 2 Covalent Bonding... pages 178-189
17
Octet Rule Exceptions• Less than 8 electrons
– Boron •Three valence electrons•Stable with only six instead of eight
– Beryllium•Two valence electrons•Stable with only four instead of eight
Always!!Always!!
Chapter 6 Section 2 Covalent Bonding... pages 178-189
18
Octet Rule Exceptions• Expanded valence - involves the d
orbitals as well as s & p– Phosphorus
•Five valence electrons•Stable with only ten instead of eight
– Sulfur•Six valence electrons•Stable with only twelve instead of eight
Not Always!!
Not Always!!
Chapter 6 Section 2 Covalent Bonding... pages 178-189
21
Lewis Structures• Formulas in which the
symbols represent nuclei and inner shell electrons, dashes or dot-pairs between symbols represent covalent bonds and dots by one symbol represent unshared pairs.
• Shared pairs = a bond• Unshared pairs = a lone pear
Chapter 6 Section 2 Covalent Bonding... pages 178-189
23
Structural Formula• Indicates the type, number and
arrangement of the atoms and the bonds but not the unshared pairs
Chapter 6 Section 2 Covalent Bonding... pages 178-189
25
How to Draw Lewis Structures1. Do the math to determine the
number of bonds
C H3 I(1 x 8) +(3 x 2) +(1 x 8) = 22 e-
(1 x 4) +(3 x 1) +(1 x 7) = 14 e-
/2 = 4
_
All atoms need 8 electrons to be stable,except H which only needs 2.
All atoms have their valence electrons available for bonding.Subtract the “have” from the “need”.
Divide the total by 2 to get the number of bonds in the molecule.
8 e-
Chapter 6 Section 2 Covalent Bonding... pages 178-189
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How to Draw Lewis Structures2. Arrange the atoms as symetrically as
possible, with a central atom.
H
C is the central atom if it is present.H and halogens go on the outside.
ICHH
Chapter 6 Section 2 Covalent Bonding... pages 178-189
27
How to Draw Lewis Structures3. Connect with bonds.
H
If you have too many bonds, double or triple up.
ICHH
Chapter 6 Section 2 Covalent Bonding... pages 178-189
28
How to Draw Lewis Structures4. Add unshared pairs so that all
atoms have 8e- (except H)
H
A bond counts as two electrons.
ICHH
Try page 186 #1-4 Practice.
Chapter 6 Section 2 Covalent Bonding... pages 178-189
29
Multiple Covalent BondsSingle bond: 2 e- are shared by 2 atomsDouble bond: 4 e- are shared by 4 atomsTriple bond: 6 e- are shared by 3 atomsOccur commonly with C, N and O
STRONG single bond SHORT
STRONGER double bond SHORTER
STRONGEST triple bond SHORTESTTable on page 187
Try page 188 #1 & 2 Practice
Chapter 6 Section 2 Covalent Bonding... pages 178-189
31
Resonance Structures• Bonding in molecules that
cannot be correctly represented by a single Lewis structure.
Chapter 6 Section 2 Covalent Bonding... pages 178-189
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Lew
is S
truct
ure
s Pra
ctic
e
• C2Cl4• SCl2• AsF5
• CI2Cl2• BF3
• NO 1-
• CH2O
• IO3 1-
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