P Orbitals Flashcards
What is meant by directional and what orbitals are directional?
These are orbitals that prefer a specific orientation in space where the lobes representing electron density lie along an axis
P orbitals are directional
What does the directionality of the p orbitals mean?
This means they all interact differently
Describe the different orientations of the p orbitals
The pz orbitals are directed towards each other whereas px and py orbitals on each atom are orientated 90 degrees to each other to the direction of the other atom
Describe the inphase combination of pz orbitals
Constructive interference
End on overlap forms sigma bonding orbitals
( see diagrams)
Describe the out of phase combination of pz orbitals
Destructive interference forms sigma antibonding orbitals
There is a node in the middle of this orbital
The more nodes= higher energy
Describe the in phase combination of px orbitals
Constructive interference
Side on overlap forms pi bonding orbitals
The pi bonds have a nodal plane along the internuclear axis
Electrons are delocalised in pi clouds (increased region of electron density above and below the plane
(See diagram)
Describe the out of phase overlap of px orbitals
Destructive interference forms pi antibonding orbitals
(Side on overlap)
Node along plane and in between the orbital
What is the internuclear axis?
This is the z axis that horizontally goes through the nucleus
What is a HOMO?
Highest occupied molecular orbital
This is where electrons are donated from
What is a LUMO?
Lowest unoccupied molecular orbitals
This is where electrons are donated to
Describe sigma and pi orbitals around the internuclear axis
Sigma bonds are cyndrically symmetrical along the internuclear axis
Pi bonds have nodal plane along the internuclear axis
Why are antibonding orbitals higher in energy than bonding orbitals?
Antibonding orbitals have more nodes than sigma
Why are pi orbitals stabilised and destabilised to a lesser degree than sigma orbitals
The interaction between px, px and py, py is less effective than the interaction between pz and px and py don’t point towards each other
This means overlap is not as good
Why does BDE decrease faster for pi bonds as internuclear separation increases?
Pi overlap is more distance sensitive
Why is there no net interaction between a pz orbital and a px/y orbital?
This is because there is both a bonding and antibonding interaction (where in phase and out of phase px interacts with one phase lobe of pz orbital)
The antibonding and bonding interaction cancels out
(See diagram)
Why do sigma bonding stabilise more and sigma antibonding destabilise more than pi bonding?
This is because sigma overlap is greater than pi overlap
