Bonding, Lewis Dot Diagrams, and Molecular Geometry

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Chapter 6

• Bonding, Lewis Dot Diagrams, and Molecular
  Geometry

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3 Types of Chemical Bonds

• Metallic
• electrons flow freely from atom to atom
• Occurs between 2 metals
• Not a compound, but rather a mixture

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2. Ionic Bonds

• Transfer of electrons
• Due to LARGE difference in electronegativity (1.8
  4.0)

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Examples Identify each type of bond in each
compound using electronegativity values. Then,
draw a Lewis diagram for each compound.

• LiBr
• Na2O
• AlF3

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Properties of Ionic Compounds

• Exist as crystalline solids
• High melting points
• Can conduct electricity in molten or aqueous
  state
• Most soluble in polar solvents

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3. Covalent Bonds

• Electrons are shared
• Due to small difference in electronegativities
  (lt1.8)

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Properties of Molecular Compounds

• Typically exist as gases, liquids, or amorphous
  solids
• Low melting and boiling points
• Poor conductors
• Most soluble in nonpolar solvents

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Examples Identify the type of bond within each
compound. Draw Lewis Dot diagram for the
following molecular compounds (contain covalent
bonds).

• PH3
• SCl2

• BBr3
• CH4

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Multiple Covalent Bonds
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Examples Draw Lewis Dot diagram for the
following molecular compounds, which contain
double or triple bonds.

• O2
• CN-

• C2H2
• CH2O

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Lewis diagrams for polyatomic ions

• NH4 OH-
• CN- SF3

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Resonance more than one LDD needed to depict
structure

• Hyposulfite SO2-2
• Sulfite SO3-2
• Sulfate SO4-2

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VSEPR theory

• Valence Shell Electron Pair Repulsion electron
  pairs are arranged around central atom of a
  molecule so that they have as much space as
  possible
• Build a molecule with 2 atoms connected to
  central atom (for a total of 3 atoms) what does
  it look like?

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2 electron pairs around central atom
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3 electron pairs around central atom
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4 electron pairs around central atom
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Molecular Geometry
Example CH4 vs. NH3 vs. H2O
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Hybridization

• s and p orbitals blend together to form new
  bonding orbitals that support VSEPR shapes

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Polarity

• Nonpolar covalent bond
• Electrons are shared equally
• Difference in electronegativity from 0.0 0.3
• Ex. F2

• Polar covalent bond
• Electrons are shared unequally
• Difference in electronegativity from 0.4 1.7
• Ex. F-Br

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Nonpolar Molecules

• Completely symmetrical w.r.t. central atom
• Hint central atom will only have bonds and only
  to one element (usually)

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Polar Molecules

• Asymmetrical w.r.t. central atom
• Hint central atom has LP or 2 kinds of elements
  bonded to it

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Intermolecular Forces(also known as Van der
Waals forces)attractive forces between molecules

• London Dispersion Force (LDF) in nonpolar
  molecules movement of e- sometimes unbalanced,
  creating temporary partial charges
• Dipole-dipole partial charges of polar
  molecules attracted to one another
• Hydrogen bonding stronger version of d-d ? H
  attracted to LP of N, O, or F

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Intermolecular Forces
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Dipole-dipole
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Hydrogen bonding
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Physical Properties

• Ionic Compounds

• Molecular Compounds

• Exist as crystalline solids
• High melting points
• Can conduct electricity in molten or aqueous
  state
• Most soluble in polar solvents

• Typically exist as gases, liquids, or amorphous
  solids
• Low melting and boiling points
• Poor conductors
• Most soluble in nonpolar solvents