polyatomic MO diagrams and Walsh diagrams
see w4 videos 18-20
define hybrid atomic orbitals
the result of combining atomic orbitals to make orbitals that are appropriate to form bonds with direction and angle predicted by VSEPR
when forming HAOs, no. of atomic orbitals =
no. of HAOs
if you combine 4 atomic orbitals, you form 4 hybrid atomic orbitals
how do you make the following haos
sp
sp2
sp3
you always start with an s-orbital then add p-orbitals
s + p
s + p + p
s + p + p + p
2 similarities and 1 difference of haos of the same type, eg 2 sp haos
same energy
same overall shape
point in all different directions
sp HAOs
- how many are there
- how many bonds can be formed
- angle they point away from each other
- what happens to remaining p-orbitals
- 2: one is in phase, one out of phase
- forms two single bonds
- 180°
- remaining px and py orbitals are unhybridised and overlap to form 2 pi-bonds
sp2 HAOs
- how many are there
- how many bonds can be formed
- angle they point away from each other
- what happens to remaining p-orbitals
- 3
- forms three single bonds
- point 120° away from each other in a plane
- remaining p orbital is unhybridised overlaps to form one pi-bond
sp3 HAOs
- how many are there
- how many bonds can be formed
- angle they point away from each other
- what happens to remaining p-orbitals
- 4
- forms four single bonds
- 109.5°
- no more orbitals so forms 4 single bonds
how are hybrid molecular orbitals formed
HMOs made from overlapping HAOs with HAOs or AOds
which HAOs and HMOs are involved in the C-H bond in methane
C: is sp3 hybridised
H: just has outer 1s orbital
sp3 and 1s overlap to form a σ bonding HMO and a σ* anti-bonding HMO
see w4 vid22 for HCN example
which overlap is more constructive sigma or pi and why
sigma is more constructive
orbitals in sigma overlap point towards each other but in pi overlap they are parallel and so don’t overlap as constructively as sigma
what is meant by delocalised π-bonding in a molecule
bonding that involves out-of-plane 2p orbitals (π-bonds) from two or more atoms in the molecule
describe how benzene has delocalised π-system
- each C in benzene is sp2 hybridised
- each C has a 2p orbital that lies perpendicular to the plane of the ring
- the π MOs are formed from all 6 2p AOs
see w4 vid23 for drawings of π MOs
describe how butadiene has a delocalised π-system
- each C is sp2 hybridised
- each C a 2p orbital perpendicular to plane of the alkene
- the π MOs are formed from all four of these AOs
in the delocalised π-system in benzene, describe:
- the lowest energy MO
- the highest energy MO
- the intermediate MO
lowest energy
- all 6 2p orbitals in phase, lobes on top of the plane are same phase and lobes below the planes are the same phase
- no nodal planes
highest energy
- all 6 p orbitals are in alternating phases, adjacent p orbitals are opposite phases
- 3 nodal planes
intermediate MOs
- will have 1 or 2 nodal planes
- MOs with same number of planes are degenerate
