Chemical Bonding and Molecular Structure

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Chemical Bondingand Molecular Structure

• Chapter 12
• Sec 12.1 - 12.7

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Review

• Chemical bonds involve electrons
• Specifically, valence electrons (outer s and p
  orbitals)
• These electrons are transferred or shared in a
  molecule

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Using Electronegativity

• Large ?EN Ionic bond
• Medium ?EN Polar Covalent bond
• Small ?EN Non-polar Covalent bond
• Distance between location of elements on Periodic
  Table corresponds closely with ?EN.

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Polarity

• Bonds (and molecules) are polar if there is an
  unequal sharing of electrons

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? Means Partial Charge

• A ?- indicates a partial negative charge (near
  the more electronegative atom
• While ? is a partial positive charge

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Compare Types of Bonds
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KEY CONCEPT!

• By transferring or sharing valence electrons
• ALL bonds allow the atoms in a compound to
  achieve a
• NOBLE GAS ELECTRON CONFIGURATION

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Lewis Structures

• Provide a way to illustrate valence electrons in
  a molecule
• Allow the prediction of Molecular Geometry and
  Molecular Polarity

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Lewis Structures - Main Group Elements
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Rules for Drawing Lewis Structures

1. Find the sum of all valence electrons of atoms in
   the molecule
2. Use a pair of electrons to represent a bond
   between two atoms
3. Rearrange remaining electrons to satisfy octet
   rule (or duet rule for H)

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For an Ionic Compound

• Note that Potassium loses its valence electron to
  chlorine. The brackets indicate a negative charge
  around the chloride ion.

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For Water
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Double Bonds

• There are times when double (or triple) bonds
  are needed in a molecule so that each atom is
  surround by an octet of electrons

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Multiple Lewis Structures - Resonance
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Homework

• Complete the two Lewis Structure
• Handouts

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• Chemical Bondingand Molecular Structure
• Chapter 12
• Sec 12.8 - 12.10

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Goals

1. To use Lewis Structures as a way to predict the
   geometry of Molecules
2. Determine if molecules are polar or nonpolar

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VSEPR Model

• Valence Shell Electron Pair Repulsion Model
• Bonds (pairs of electrons) attempt to move as far
  away as possible from one another in a molecule

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This explains the Geometry of H2O

• Water is a bent molecule, because of the lone
  pairs around the central Oxygen atom

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Various Geometry of Molecules

• See Examples on Next Slides
• (Hand-Out)

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Polar or Non-polar Molecule?

• A molecule may have polar covalent bonds and not
  be polar overall
• ?????????
• Geometry must also be considered

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Ammonia (NH3) is polar

1. The bonds between hydrogen and nitrogen are polar
   covalent (?EN .87)
2. Pyramidal geometry of molecule points charges
   toward N

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Carbon Dioxide is Non-polar

• Even though the bonds between carbon and oxygen
  are polar covalent (?EN 1.0), the pull of
  electrons is in equal and opposite directions
  because CO2 is linear

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Water is Wacky!
Water has some strange properties due to its
structure
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