Finish presentations

1
Agenda

• Finish presentations
• Short lecture reinforcing yesterdays group
  presentations
• Questions?

2
Polyatomic Ions

• Covalently bonded ionic molecules
• Molecules have more valence electrons than they
  should
• When drawing Lewis structures Look for a
  pattern in other molecules you know
• For example PO43- should look just like CH4,
  because both have 4 atoms surrounding a central
  atom
• LOOK FOR PATTERNS

3
Octet Exceptions

• Some elements can form suboctetsless than 8
  electrons
• Theyre very reactive
• Coordinate covalent bondsa lone pair from a
  molecule is donated to another atom or ion to
  form a bond so the other atom/ion has a filled
  valence shell
• Expanded octetssome elements can form more than
  4 bonds (more than 8 valence electrons) because
  they can use d-orbitals

4
VSEPR model

• Electrons try to stay away from each other
  because they have the same charge
• They exist in 3-d, and according to the VSEPR
  model they have fixed bond angles because of
  repulsion
• Unshared pairs are in larger orbitals that push
  together bonding electrons

5
Hybridization

• When atoms covalently bond, they form hybrid
  orbitals
• Hybrid orbitals are neither s nor p, but a
  mixture of both
• Video on next page that explains

6
Molecular shapes

• Heres what you need to know
• 3 elements, no electron pairs on central atom
  linear
• 4 elements, no electron pairs on central atom
  trigonal planar
• 5 elements, no electron pairs on central element
  tetrahedral
• 4 elements, one electron pair on central atom
  trigonal pyramidal
• 3 elements, two electron pairs on central atom
  bent

7
Molecular Shapes

• Heres what you need to know
• 3 atoms, no electron pairs on central atom
  linear
• 4 atoms, no electron pairs on central atom
  trigonal planar
• 5 atoms, no electron pairs on central element
  tetrahedral
• 4atoms, one electron pair on central atom
  trigonal pyramidal
• 3atoms, two electron pairs on central atom bent

• What shape will the following have
• 1. BF3
• 2. OCl2
• 3. CO2
• 4. CF4