Chemical Bonding

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• Chemical Bonding

• Chapter 6
• Section 1 2
• Pages 175-189

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Chemical Bond

• Attractive force between atoms or ions that
  binds them together as a unit.(valence e- of one
  atom attracted to the nucleus of
  another atom).
• Bonds tend to form to decrease potential
  energy or increase stability.
• Types are ionic or covalent.

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Ionic Bond
A cation is attracted to an anion

• Cation positively charged ion
• Anion negatively charged ion

Octet Rule is followed!
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Ionic Compounds
Tend to form a crystal lattice.
Highly ordered
Repeating pattern
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Ionic Compound metal-nonmetal
Two or more elements are combined in a chemical
bond by gaining or losing electrons that achieves
the octet rule.
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Covalent Bonding nonmetal-nonmetal
A covalent bond is formed by a shared pair of
electrons between two atoms.
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Electronegativity

• Using Electronegativity values one can determine
  the ionic character.
• Nonpolar-covalent, equal sharing of electrons.
  Bonds having 0 to 5 ionic character.
  Electronegativity differences of 0 to 0.3.
• Polar-covalent, unequal sharing of electrons.
  Bonds having 5 to 50 ionic character.
  Electronegativity differences between 0.3 to 1.7.
• Ionic bonding, is a complete transfer of
  electrons. gt50 ionic character.
  Electronegativity differences of 1.7 to 3.3

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Molecule nonmetal-nonmetal
A group of atoms united by covalent bonds. (
polar or non-polar covalent).
Diatomic Molecule
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Molecular Substances
Substance made of molecules
DNA
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The law of Octet
Octet Rule
Atoms tend to gain, lose, or share electrons in
order to get a full set of valence electrons.
(usually 8 electrons)
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Bond Length

• Increases as you go down a group, because the
  atomic radius increases.
• Shorter for multiple bonds.

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Multiple Bond Length

• Triple bond is shorter than double bond, which is
  shorter than single bond.
• Why? The more electrons in a bond, the stronger
  the attraction to the positively charged nuclei
  of the bonding atoms.

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Bond Energies KJ/mol

• Bond Energies- The amount of energy required to
  break a chemical bond and form neutral isolated
  atoms.
• In general the higher the bond energy required
  the stronger the attraction, the shorter the
  chemical bond. (Data table on page 182)

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Exceptions to the Octet Rule

• Exceptions are those that form bonds that either
  have less than 8e- or more than 8e-
• Less than eight
• Hydrogen can form one bond that has 2e-
• Boron forms three bonds that contains 6e-
• More than eight
• Sulfur can form 6 bonds containing 12e-
• Phosphorus can form 5 bonds containing 10e-

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Lewis Structures
Lewis Dot Diagrams

• The use of dots or other symbols to represent
  bonded and unshared electrons.

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Structural (lines 2e- )
2 shared electrons make a bond.
Lines show the bond between atoms in a compound.
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How to Draw Lewis Structures
Step 1 (N) determine the number of electrons
Needed for each atom in the compound. Grps
14,15,16,17 all need 8. Hydrogen needs 2. Step
2 (A)determine the number of electrons Available,
which is determined by the grp . Step
3 N A e- Shared (S) Step 4 A - S Unshared
(U)
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Step 1 Electrons Needed N
Example Methane CH4
4(2) 1(8) 16e-
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Step 2 Electrons Available A

• 1(4) 4(1) 8e-

Carbon goes in the middle because it is the
singular atom.
H
C
H
H
H
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Step 2 N A S
Bonds go between atoms Each bond uses up 2
electrons

• 16 8 8e- Shared

H
C
H
H
H

4 Bonds use up 8 electrons (4 x 2 8) Unshared
? 8 8 0
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Step 1 Ammonia NH3
Step 1 determine N Step 2 determine A Step 3 N
A S Step 4 A S U

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Arrange Atoms
Nitrogen goes in the middle because it is the
singular atom.
H
N
H
H
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Step 2Form Bonds
Bonds go between atoms (6e-) Each bond
uses up 2 e-
H
N
H
H


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complete the octet

• N 14
• A 8
• S 6
• A S 2
• Used up 6e- with bonds
• 2 unshared to complete the octet
• Youre done!

H
N
H
H


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Example Formaldehyde CH2O
Step 1 N Step 2 A Step 3 N A S Step 4 A S
U

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Arrange Atoms
You would have to guess whether C or O goes in
the middle? It is Carbon, because it can form
the most bonds, and least electronegative!
H
C
O
H
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Form Bonds
Bonds go between atoms Each bond uses up 2
electrons
H
C
O
H


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Step 3Distribute remaining electrons

• Had total of 20e- from step 1
• Used up 6e- with bonds
• Need 2 more e- on C
• Need 6 more e- on O
• NOT ENOUGH TO GO AROUND NEED DOUBLE BOND.

H
H
O
C

Need 2 more e- on carbon to complete octet!

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Double Bonds

• Remember the Octet Rule !
• Carbon Oxygen both need 8e-.
• They get 8 by sharing 4 e- between them.

H

H
O
C



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Double Bonds
H

• Represent double bond with a double line.
• You are done!

H
O
C


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Multiple Bonds

• Double bonds occur in these molecular compounds
  
• Oxygen, Carbon Dioxide
• Triple Bonds Nitrogen

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Resonance Structures

• Molecules that cant be correctly represented by
  a single Lewis diagram.
• Actual structure is an average of all the
  possibilities.
• Show possible structures separated by a
  double-headed arrow.

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Example SO3