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Chemical Bonding

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Chemical Bonding Chapter 6 Section 1 & 2 Pages 175-189 – PowerPoint PPT presentation

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Title: Chemical Bonding


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

2
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.

3
Ionic Bond
A cation is attracted to an anion
  • Cation positively charged ion
  • Anion negatively charged ion

Octet Rule is followed!
4
Ionic Compounds
Tend to form a crystal lattice.
Highly ordered
Repeating pattern
5
Ionic Compound metal-nonmetal
Two or more elements are combined in a chemical
bond by gaining or losing electrons that achieves
the octet rule.
6
Covalent Bonding nonmetal-nonmetal
A covalent bond is formed by a shared pair of
electrons between two atoms.
7
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

8
Molecule nonmetal-nonmetal
A group of atoms united by covalent bonds. (
polar or non-polar covalent).
Diatomic Molecule
9
Molecular Substances
Substance made of molecules
DNA
10
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)
11
Bond Length
  • Increases as you go down a group, because the
    atomic radius increases.
  • Shorter for multiple bonds.

12
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.

13
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)

14
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-

15
Lewis Structures
Lewis Dot Diagrams
  • The use of dots or other symbols to represent
    bonded and unshared electrons.

16
Structural (lines 2e- )
2 shared electrons make a bond.
Lines show the bond between atoms in a compound.
17
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)
18
Step 1 Electrons Needed N
Example Methane CH4
4(2) 1(8) 16e-
19
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
20
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
21
Step 1 Ammonia NH3
Step 1 determine N Step 2 determine A Step 3 N
A S Step 4 A S U

22
Arrange Atoms
Nitrogen goes in the middle because it is the
singular atom.
H
N
H
H
23
Step 2Form Bonds
Bonds go between atoms (6e-) Each bond
uses up 2 e-
H
N
H
H


24
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


25
Example Formaldehyde CH2O
Step 1 N Step 2 A Step 3 N A S Step 4 A S
U

26
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
27
Form Bonds
Bonds go between atoms Each bond uses up 2
electrons
H
C
O
H


28
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!

29
Double Bonds
  • Remember the Octet Rule !
  • Carbon Oxygen both need 8e-.
  • They get 8 by sharing 4 e- between them.

H

H
O
C



30
Double Bonds
H
  • Represent double bond with a double line.
  • You are done!


H
O
C


31
Multiple Bonds
  • Double bonds occur in these molecular compounds
  • Oxygen, Carbon Dioxide
  • Triple Bonds Nitrogen


32
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.

33
Example SO3
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