Lecture 3 Flashcards
What happens when 2 1s orbitals with the same phase overlap?
- forms sigma bonding molecular orbital
- build up of electron density
- draw diagram from pg 24 of handout
Draw the pictorial reps of sigma bonding molecular orbital and describe them
- Atomic orbitals= R(r) plots for the AOs of the 2 H atom that will interact
- Molecular orbital= turn on interaction- constructive interference
- wavefunction^2- extra probability of finding the electrons between nuclei, lower energy
Give the mathematical rep for sigma bonding molecular orbital
What happens when 2 1s atomic orbitals with different phases overlap?
- forms sigma* antibonding orbital
- 2 atoms repel and form node in the middle with 0 electron density
- draw diagram from pg 25 in handout
Draw the pictorial reps of sigma* antibonding orbital and describe them
- Atomic orbitals= R(r) plots for 2 H atoms before interaction
- Molecular orbital= turn on the interaction- destructive interference
- wavefunction^2- reduced electron density. Higher energy than just 2 Hs on their own
Give the mathematical rep for sigma* antibonding orbital
Describe bonding MOs
- Lower in E than 2 separate AOs (Stabilised)
- Formed by in-phase combination of AOs
- Build up of electron density between the nuclei of the 2 atoms
Describe antibonding MOs
- Higher in E than 2 separate AOs (Destabilised)
- Formed by out-of-phase combination of AOs
- Reduction in electron density between the nuclei of the 2 atoms (node)
Give the general rules for building up a molecular orbital energy diagram
- E axis on LHS
- AOs on the 2 sides
- MOs on the middle
- Show the electrons on the MOs they occupy
- Dashed lines to connect the AOs and MOs
What do sigma orbitals looks like?
- MO thats spherically symmetric around the internuclear axis (build up in electron density between the nuclei)
What do sigma* orbitals look like?
- MO that’s spherically symmetric around the intermolecular axis- reduction in electron density between nuclei
What is the Aufbau principle?
lowest energy MO is always occupied first
What is the Pauli Principle?
- 2 electrons maximum number in each orbital.
- must have opposite spins (spin is defined by the quantum number, ms
ms= +-1/2)
What is Hund’s rule?
parallel spins are preferred if degenerate orbitals are available
Define bond order
the number of electrons in bonding MOs minus the number of electrons in antibonding MOs divided by 2
