Exceptions to the Octet Rule
- Atoms balance octet rule and having a net zero charge
Hydrogen is content with having two electrons total.
Atoms with more than 8 electrons in lewis structure
- 3rd period, have empty d3 orbitals
- Bonded with very electronegative atoms (O, F, Cl)
- The atom breaking the octet rule is less electronegative than the atoms it's bonded to.
- Then
- O,F,Cl pulls electrons close
- Can pull electrons from bonded atom up into the 3rd orbital
Sulfur gets electrons pulled into the 3d orbital, electrons have higher potential energy further from the nucleus. Sulfur with electronegative atoms, sulfur is hypervalent. $$SO_4$$ lewis structure is happy with net neutral charge.
Three-Dimensional Geometry
Geometry is based on:
- Number of electron density domains around the central atom
- Want to be as far apart as possible because electron charges repel.
- Electrons domains - bonding 1 e.d. per bond regardless of bond order.
- Non-bonding 1 e.d per electron pair or radical.
- VESPR Theory
- Predict most stable electron domain / molecular geometry.
- Electron Domain Geometry
- Every electron domain around the central atom.
- Molecular Geometry
- Only bonding domains around the central atom.
Electron Domain Geometries
- 2 Electron Domains
-
Linear
-
- Bond Angle
- 180deg
- 3 Electron Domains
-
Trigonal Planar
-
- Bond Angle
- 120deg
- 4 Electron Domains
-
Tetrahedral
-
- Bond Angle
- 109.5deg
- 5 Electron Domains
-
Trigonal Bipyramidal
-
- Bond Angle
- 90deg/120deg
- 6 Electron Domains
-
Octahedral
-
- Bond Angle
- 90deg
Wedge and Dash Projections
- Solid line represents same plane as the paper.
- Bold wedge extends out of the central atom toward you.
- Dashed wedge extends further into the paper/desk.
Double bonds/triple bonds should always be oriented to be on the same plane as the paper.
- Molecular Geometry
- Only considers the location of bonds.
If no lone pairs/electrons = e.d. = m.d.g.
Lone pairs on the central atom result in "less than [ideal bond angle]" because they exert repulsive force on the central atom.
Molecular Geometry
- 2 Electron Domains
- Linear
- 3 Electron Domains
- Trigonal Planar (0 lone pairs)
- Bent (1 lone pairs)
- 4 Electron Domains
- Tetrahedral (0 lone pairs)
- Trigonal Pyramydal (1 lone pairs)
- Bent (2 lone pairs)
Central atom has the highest bonding capacity.
Functional Groups
- Ketone
- ?
- Aldehyde
- ?
- Carboxyl
- ?
- Alkoxy
- ?
- Amine
- ?
- Phenyl
- ?
- Hydroxyl
- ?
- 'R' in lewis structure represents the rest of the molecule.
- Skeletal Structures
- Every bend and end represents carbon + however many H its bonded to in order to reach whole octet.
- Butane
- ?
- Butene
- ?
- Ethanol
- ?
Hybridization
- Model to combine domains around atom in covalent bonds.