SECTION 4 - CHEMICAL BONDING II Flashcards
VSEPR
Valence shell electron repulsion theory that tells us the 3 dimensional shape of a molecule
Electron group geometry (egg)
Based on the number of electrons surrounding central atom (bonded atoms + lone pairs)
5 basic electron group geometry shapes
- Linear (2 e)
- Trigonal planar (3 e)
- Tetrahedral (4 e)
- Trigonal bypyramidal (5 e)
- Octahedral (6 e)
Dash lines
Extend BEHIND plane
Solid thick lines
Protrude OUT plane
Molecular shape (mg)
Only count atoms bonded to central atom
egg = mg
When all electron groups are atoms
egg doesnt equal mg when
Lone pairs present
5 molecular geometry shape
- Bent
- Seesaw
- T shape
- Square pyramidal
- Square planar
BLT
BP LP
2 1
2 2
BENT
2 3
LINEAR
3 1
TRIGONAL PYRAMIDAL
3 2
T SHAPE
4 1
SEESAW
4 2
SQUARE PLANAR
5 1
SQUARE PYRAMIDAL
Axial bonding position
Up/down
Equatorial bonding position
Horizontal/diagnol
- LP go on equatorial
Dipole moment
Measure of molecular polarity with unit of Debye (D). 1D = 3.34x10^-30cm
Dipole moment in diatomic molecule
There is only 1 bond so the dipole determined by bond
Dipole moment in polyatomic molecule
The total polarity determined by bond polarity and bond angle
Arrows facing out from one another
U = 10 (not polar)
Arrows facing towards each other
Polar
Valence bond theory
Tells us how electrons interact to hold atoms together into molecules and defines covalent bonds as electron density between 2 atoms as a result of constructive interference
Ideal distance of valence bond theory
Occurs with overlap between partially filed atomic bonds on each atom and the overlap creates new covalent bond
Inphase
Atoms that are in phase will overlap constructively and form bond
Outphase
Atoms that are out phase creates region of 0 electron density (node)
Node
N-1 (region of 0 electron density)
Sigma bond (3)
- Formed by overlap of atomic orbitals head to head
- All single bonds are sigma bonds
- Free rotation allowed
Pi bond (5)
- Formed by overlap of p orbitals side to side
- Multiple bonds consists of one sigma bond and some pi bonds
- Contains 2 regions of electron density
- Rotation not allowed
- Overlapping must occur in similar phase orbitals
Sp hybridization
2 electron groups
Sp2 hybridization
3 electron groups