HL4-4.ppt

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HL4-4.ppt

• Orbital Hybridizations Molecular Shapes
• 14.2.3

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14.2.3

• Identify and explain the relationships between
  Lewis structures, molecular shapes and types of
  hybridization (sp, sp2 and sp3).
• Well start with a quick review of hybridization
• ATOMIC ORBITALS OVERLAP TO FORM 2 TYPES OF
  COVALENT BOND
• d and p

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Bond Orders Hybridization

• Single Bond sp3 hybridization
• A d bond
• Double Bond sp2 hybridization
• A d bond a p bond
• Triple Bond sp hybridization
• A d bond 2 p bonds

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Hybridization Geometry

• If an s orbital is sphere shaped and 3 p orbitals
  are dumbbell shaped and at 90 to each other,
  they clearly must undergo some change to get 4
  sp3 orbitals that are at 109 to each other.
• Hybrid orbitals are not only used to explain the
  appearance of degenerate orbitals.
• They also can be used to explain the geometries
  predicted by VSEPR theory.

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Sigma (d) Bonds

• Remember that sigma bonds are formed between 2 s
  orbitals and have linear/axial symmetry.

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Pi (p) bonds

• When a sigma bond is formed by direct orbital
  overlap and this brings two parallel 'p' orbitals
  into close proximity then these can overlap
  sideways (laterally) to form a region of electron
  density that is not directly between the two
  nuclear centers but which nevertheless
  contributes to bonding. This is called a pi bond.

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Why hybridize?

• It seems that the orbitals used for bonding are
  arranged as far apart as possible suggesting that
  they have the same energy (degenerate). We know
  that the orbitals on the carbon atom do not have
  the same energy
• the 2s orbital is of lower energy that the three
  2p orbitals.

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Why hybridize?

• Hybridisation is a model that allows us to
  combine the atomic orbitals and then produce four
  degenerate orbitals to be used for bonding.

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Why hybridize?

• In order for the electrons to be ready for this
  process one of them must be promoted from the 2s
  orbital to the 2pz orbital as in the diagram.

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The sp3 hybrid orbital

• As these new orbital have emerged from one s and
  three p orbitals they are called 'sp3' orbitals.

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Other types of hybridization

• Carbon can also bond to three other atoms instead
  of four (as in methane) and it seems that it
  hybridised its orbitals using only the 2s and two
  of the 2p orbitals to do this.

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Other types of hybridization

• How would an sp hybridization work?

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Hybridization Geometry

• Now that weve looked at the hows and whys, it is
  time to try and visualize
• See the animations below.
• http//ibchem.com/IB/ibnotes/full/bon_htm/hybrid.h
  tm
• The following slides show the combinations of
  atomic orbitals giving rise to each type of bond.

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s overlapping an s

• Type of bond sigma
• Example H-H in H2

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s overlapping a p

• Type of bond sigma
• Example H-Cl in HCl

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p and p end-on

• Type of bond sigma
• Example Cl-Cl in Cl2

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hybrid orbitals and an s

• Type of bond sigma
• Example C-H in CH4

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hybrid orbitals with hybrid orbitals

• Type of bond sigma
• Example one of the CC in C2H4

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p and p sideways

• Type of bond pi
• Example the other CC in C2H4