Times Symbol Blank Valence Shell Electron Pair Repulsion

1
Valence Shell Electron Pair Repulsion Theory

• Electron pairs in the valence shell of the
  central atom repel each other and align
  themselves to minimize this repulsion

2
VSEPR Theory

• Applied to covalent bonding only.
• Applied to Representative Elements only
• Quantum Mechanics
• Electron interactions between bonded atoms effect
  the j2 function changing the orbital shape.
• Definitions- define the terms below
• Ligand
• Shared Pair (Bonding Pair)
• Unshared Pair (Unbonded Pair or Lone Pair)

3
VSEPR Theory

• Electron Pair Geometry- Describes how the
  electron pairs align around the central atom to
  create a 3-D shape.
• Molecular Geometry- Describes how the atoms
  bonded to the central atom align around the
  central atom to create a 3-D shape.
• Sigma bonds and lone pairs around the central
  atom are used to determine the Electron Pair
  Geometry. Pi bonds do not affect the angles
  between the ligands and central atom because
  electrons in Pi bonds are not in the same plane
  as the Sigma bonds and lone pairs.

4
Draw the Lewis Dot Structure for each of the
following Compounds. Split into groups, each
group show the Lewis Dot Structure on the board.
Record all the answers on this sheet keeping rows
of compound together.

• BeI2, CO2 and HCN
• BBr3, SO3, SO2
• CCl4 and PBr3
• PBr5
• SCl6

• Linear EPG
• Trigonal Planar EPG
• Tetrahedral EPG
• Trigonal Bipyramidal EPG
• Octahedral EPG

5
Five Electron Pair Geometries-A balloon
represents a region of space for a bonding or
nonbonding pair of electrons around the central
atom. Pi Bonds are not shown in these pictures.
Linear
Trigonal Planar
Tetrahedral
Trigonal Bipyramidal
Octahedral
6
Molecular Geometry and Electron Pair Geometry are
the same when there are no unshared pairs of
electrons around the central atom.

• Linear- 2 pair of electrons (or groups) around
  the central atom
• Trigonal Planar- 3 pair of electrons (or groups)
  around the central atom
• Tetrahedral- 4 pair of electrons (or groups)
  around the central atom
• Trigonal-bipyramidal- 5 pair of electrons around
  the central atom
• Octahedral - 6 pair of electrons around the
  central atom
• List the formula of the molecules that do not
  have lone pairs of electrons under the
  appropriate Molecular Geometry.

7
Molecular Geometry - Unshared Pairs of electrons
distort the shape. EPG remains unchanged but
different names are given to the Molecular
Geometry which describe how the atoms bonded to
the central atom align around the central atom.

• Consider the Molecular Geometries for the
  Tetrahedral EPG
• No unshared pairs- tetrahedral (Methane)
• One unshared pair- pyramidal ( Ammonia)
• Two unshared pairs- angular or bent (Water or
  Oxygen difluoride)

8
Expanded Valence Molecules- Molecular Geometry -
Unshared Pairs of electrons distort the shape.
EPG remains unchanged but different names are
given to the Molecular Geometry which describe
how the atoms bonded to the central atom align
around the central atom. P. 362

• PF5, SF4, ClF3, XeF2
• SF6, BrF5, XeF4

9
Why do we need the Valence Bond Theory? -
Consider the bond angle for the various EPGs.

• Valence Bond Theory - as the ligands approach the
  atomic orbitals of the central atom mix to create
  hybrid orbitals. The hybrid orbitals hold the
  electrons that are used for sigma bonds and for
  unbonded pairs. NOT for pi bonds.
• Consider mixing paint
• 1 Red 1 White --gt
• 1 R 1 W 1W--gt
• Consider mixing pure orbitals (Note the shape and
  number of hybrids made.)
• 1s 1p --gt
• 1s 1p 1p --gt

10
Valence Bond Theory VSEPR Theory- Hybrids and
Electron Pair Geometries
11
Formation of Hybrid Orbitals using Pure Atomic
Orbitals

• Consider H2O
• Write the electronic configuration of O.
• Write the Lewis Dot Structure and determine the
  electron pair geometry for water.
• Show the electronic configuration of O with
  hybrid orbitals.
• Draw a picture of the H2O molecule showing the
  overlap of the hybrid orbitals.

• Conside HCN
• Write the electronic configuration of C.
• Write the Lewis Dot Structure and determine the
  electron pair geometry for hydrogen cyanide.
• Show the electronic configuration of C with
  hybrid orbitals.
• Draw a picture of the HCN molecule showing the
  overlap of the hybrid orbitals.

12
Double bonds- Cis and Trans Isomers.

• Consider the compound Cl2C2F2.
• Write the electronic configuration of C.
• Write the Lewis Dot Structure and determine the
  electron pair geometry for dichlorodifluoroethene.
  
• Show the electronic configuration of C with
  hybrid orbitals.
• Draw a picture of the Cl2C2F2. molecule showing
  the overlap of the hybrid orbitals. Show the
  trans-isomer.

• Consider the compound Cl2C2F2.
• Write the electronic configuration of C.
• Write the Lewis Dot Structure and determine the
  electron pair geometry for dichlorodifluoroethene.
  
• Show the electronic configuration of C with
  hybrid orbitals.
• Draw a picture of the Cl2C2F2. molecule showing
  the overlap of the hybrid orbitals. Show the
  cis-isomer.

13
Bond Polarity and Molecular Polarity

• Bond Polarity - degree of equality for the
  sharing of electrons in a bond (e distribution in
  a bond.)
• Page 350 EN Table
• Electronegativy Difference
• .5 nonpolar covalent
• .5-gt1.7 polar covalent
• 1.7 ionic
• Show the delta, ?, notation

• Molecular Polarity- distribution of electrons in
  the molecule (lopsided, ? and ?-, polar
  molecule.
• No relationship between bond polarity and
  molecular polarity Consider NBr3 (3.0, 2.8),
  SiCl4 (1.8, 3.0)
• Dipole Moment Notation
• Expanded valence - XeF4