FINAL - SECTION 4 Flashcards
5 basic electron groups (egg)
- Count the number of electron groups around central atom (bonded atoms + LPo central)
- 2 electron groups = linear (sp)
- 3 electron groups = trigonal planar (sp2)
- 4 electron groups = tetrahedral (sp3)
- 5 electron groups = trigonal bypyramidal (sp3d)
- 6 electron groups = octahedral (sp3d2)
Dashed lines
Behind plane
Solid line
Infront of plane
7 molecular geometry shapes (mg)
- Only count ATOMS bonded to central atom
- Bent
- Linear
- Trigonal pyramidal
- T shape
- Seesaw
- Square planar
- Square pyramidal
egg = mg when
All electron groups are atoms
egg ≠ atoms when
LP are present
BLT sandwich
BP LP
2 1 Bent
2 2
2 3 Linear
3 1 Trigonal pyramidal
3 2 T shape
4 1 Seesaw
4 2 Square planar
5 1 Square pyramidal
In diatomic molecules..
Only 1 bond so the bond dipole determines polarity
In polyatomic molecules…
The total polarity is determined by bond polarity and bond angle
Valence bond theory
Defines covalent bond as an electron density between 2 atoms and the ideal distance occurs with overlap from partially filled atomic orbitals of each atom
Sigma bond
Formed head to head by overlap of orbitals (single bonds always)
Pi bond
Formed by lateral overlap of 2 lobes of orbital
Sigma and pi bond in bonds
- Single bond = 1 sigma bond
- Double bond = 1 sigma bond + 1 pi
- Triple bond = 1 sigma bond + 2 pi
Hybridization clues
- Attached to 2 atoms: sp
- Attached to 3 atoms: sp2
- Attached to 4 atoms: sp3
- Attached to 5 atoms: sp3d
- Attached to 6 atoms: sp3d2
Molecular orbital theory
Typically used for diatomic molecules or at lease treat it like that (only on valence electrons
Bonding molecular orbital
High electron density
Antibonding molecular orbital
0 electron density
*
High energy antibonding orbital
Bond order formula
Bonded electrons - anti bonded electrons/2
Bond order 1
Single bond
Bond order 2
Double bond
Bond order 3
Triple bond
Bond order 1/2
Rare usually on H2
What does high bond order mean
Strong bond
HOMO
Highest energy orbital (has electrons)
LUMO
Lowest energy orbital (no electrons)
There are 2 versions of molecular orbitals. Why
One of them is for atomic numbers less than 8, the other is atomic numbers 8 or more
MO is usually for diatomic molecules so how would you know which versions of diagram to use in an occasion like OF?
Calculate the average and the less electronegative one goes on the left and more electronegative goes on the right
Draw both MO
ok
Relationship between bonding MO and anti bonding BO energy
Antibonding MO is stronger. so sigma 2p<sigma 2p, and pi2p < pi2p
Condensed phase
Solid and liquids are considered condensed phase because they are packed close together but still vibrate
Intramolecular force
Force that binds atoms making up molecules
Intermolecular force
Force between a molecule
3 types of intermolecular force
- Dispersion
- Dipole-dipole
- H bond
Dispersion
Every molecule has it and is the weakest (exhibits small partial charges)
Dipole-dipole
Has a partial positive and partial negative. The more polar it is, the stronger dipole it has = high boiling point (harder to pull apart)
H bond
Strongest and occurs when a partially positive H is covalently bonded to small electronegative N, O, F
Order of increasing strength intermolecular force
London dispersion –> dipole-dipole –> H-bond
