Chemical Bonding

1
Chemical Bonding
2
Ions

• Cations Atoms that have lost electrons and
  result in a positive () charge
• Anions Atoms that have gained electrons and
  result in a negative (-) charge

3
Chemical Bonds

• Compound are formed from chemically bound atoms
  or ions
• Bonding only involves the valence electrons

4
Chemical Bonds

• Defn force holding two atoms together
• How are they formed?
• Atoms gain, lose, or share valence electrons
• Why does bonding occur?
• Stability achieve octet rule

5
Electron Dot Structure

• Shows valence electrons around atomic symbol

hydrogen
(group 1)
H



N


nitrogen
(group 15)




(group 17)
Cl

chlorine



6
Types of Chemical Bonds

• 3 Types
• covalent bond
• ionic bond
• metallic bond

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Ionic Bond

• Defn force holding cations and anions together

A

B

A
B-

Ionic bond
8
Ionic Bond

• Where are these bonds found?
• Ionic Compounds

9
Covalent Bond

• Defn two atoms share one pair of electrons

Electrons shared

A

B

A
B

10
Covalent Bonds

• Where are these bonds found?
• - molecules (molecular compounds)
• - polyatomic ions

11
Metallic Bonding

• Defn attraction of metallic cations

Occurs only in metals
12
Covalent Bonding

• Whats going on?
• Molecule formed when 2 or more atoms bond
  covalently

Sharing of electrons
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Two Types of Covalent Bonds

• i) nonpolar covalent equal sharing of e-
  resulting from similar electronegativities.
• ii) polar covalent UNequal sharing of e-
  resulting from different electronegativities

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Nonpolar vs. Polar
NONPOLAR
POLAR
15
Nonpolar vs. Polar
16
Nonpolar vs. Polar
17
Single Bond

• Defn one pair (2) of e- shared
• Lewis Structures represents how atoms in
  molecules are arranged
• atoms MUST obey octet rule (except hydrogen)

18
Lewis Structures

• bonded electrons occur between bonded atoms

A
B
A
B
or

single bond
19
Lewis Structures

• Unshared or Lone Pairs electron pairs NOT
  involved in bonding

A
B
A
B





lone pairs
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Lewis Structures Examples

• H2O

(8 valence e- or 4 pairs)










O
H
H
H
O






H



O
H

H
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Lewis Structures Examples

• NHF2

(20 v.e. or 10 pairs)














N
F
F
F


















H
N
H





F











N
F
F






H
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Multiple Covalent Bonds

• Double Bond two pairs (4) e- shared

A
B
A
B


O2
(12 v.e. 6 pairs)














O









O
O
O
O
O



















O
O


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Multiple Covalent Bond

• Triple Bond three pairs (6) e- shared

A
B
A
B



N2
(10 v.e. 5 pairs)



















N


N


N
N
N
N














N
N



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Comparing single, double, and triple bonds

• Bond Strength
• Bond Length

Triple gt Double gt Single
Single gt Double gt Triple
The shorter the bond, the stronger it is
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Ionic Bonding
giving/taking of valence electrons

• Whats going on?
• If I gave you a compound, how can you tell if it
  is ionic or not?
• combo of metal nonmetal

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Formation of Ionic Bonds

• NaCl

1-






Na
Cl
Na1





Cl







2s22p63s1
3s23p5
2s22p6
3s23p6
8 v.e.
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Formation of Ionic Bonds

• CaBr2

1-







Ca
Br




Br







Ca2





Br
1-







Br




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Using electronegativity to determine bond type

• Recall electronegativity how much an atom wants
  electrons
• Each atom is assigned a number between 0-4.0 to
  determine electronegativity strength

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Using electronegativity to determine bond type

• We know 3 types of bonds
• - nonpolar covalent
• - polar covalent
• - ionic
• To determine bond type, subtract
  electronegativity values and see scale

33
Scale
Using electronegativity to determine bond type
polar covalent
nonpolar covalent
ionic
1.7
0.3
0
4.0
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Using electronegativity to determine bond type
H and Cl
3.0 2.1
0.9
polar covalent
C and S
2.5 2.5
0
nonpolar covalent
Na and F
4.0 0.9
3.1
ionic
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Metallic Bonding

• Defn bond formed from attraction between
  positive nuclei and delocalized electrons
• holds metals together
• Delocalized Electrons electrons detached from
  parent atom
• lost electron away from home

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Electron Sea Model

• Defn electrons move freely within other
  molecular orbitals

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Properties of Metals

• Electron sea model gives metals certain physical
  properties
• Shiny due to photoelectric effect
• Conduct electricity and heat electrons move
  easily from one place to another
• Malleable (pound into sheets)
• Ductile (put into wires)

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Why malleable and ductile?
atoms can also move from one place to another and
still remain in contact with and bonded to the
other atoms and electrons around them
Shape 1
Shape 2
shifted atoms
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VSEPR

• Valence Shell Electron Pair Repulsion
• Defn determines the shape of molecule
• Electron pairs try to stay far away as possible

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lone pairs
atoms bonded to central atom
shape
4
0
tetrahedral
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Tetrahedral
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lone pairs
atoms bonded to central atom
shape
4
0
tetrahedral
trigonal pyramidal
1
3
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Trigonal Pyramidal
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lone pairs
atoms bonded to central atom
shape
4
0
tetrahedral
trigonal pyramidal
1
3
2
2
bent
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Bent
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lone pairs
atoms bonded to central atom
shape
4
0
tetrahedral
trigonal pyramidal
1
3
2
2
bent
trigonal planar
3
0
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Trigonal Planar
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lone pairs
atoms bonded to central atom
shape
4
0
tetrahedral
trigonal pyramidal
1
3
2
2
bent
trigonal planar
3
0
2
0
linear
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Linear