Week 4 Flashcards
As atoms come together…
Electrons begin to be shared between two nuclei (covalent bond). Wavelength is increased, so energy is decreased
When nuclei are too close together, nuclei repel each other
Equilibrium bond distance
lowest energy position of two atoms that are sharing their electrons
approximately 1 Å
The Ångström (Å)
unit of distance that we use to discuss atomic distances.
how many electrons can occupy each atomic orbital?
2
When two 1s orbitals in the same phase mix…
result is an orbital with lower energy
When two 1s orbitals in the opposite phase mix…
result is an orbital with a node, i.e. higher energy
Sigma (σ) orbitals and bonds
Looking along the bond axis, these orbitals look round, like s orbitals.
Without a node
H2 molecule
- The electrons from each H atom are in the σ bonding orbital.
- The electrons in H2 have lower energy than the electrons in 2 H atoms.
He2 dimer
- the 4 electrons fill both the bonding and antibonding orbitals.
- The electrons in He2 do not have lower energy than the electrons in 2 He atoms > this molecule does not form.
The He2+ cation
- the bonding orbital has 2 electrons and the antibonding orbitals has 1.
- The electrons in He2+ have lower energy than the electrons in 1 He atom and 1 He+ ion atoms > this molecule can be observed
Li2
- 1s orbitals do not contribute to bonding, because both the bonding and antibonding orbitals are completely filled and hence cancel.
- Only valence electrons determine bonding.
Molecular orbitals of Be2
- Electrons fill both the bonding and antibonding orbitals.
- Electrons in Be2 do not have lower energy than the electrons in 2 Be atoms -> this molecule is not stable.
mixing p orbitals
Different orientations
1. Px
2. Py
3. Pz
* 1 pair: end-on interaction
* 2 pairs: side-on interaction
Pi (𝜋) orbitals and bonds
- Those with a node in the plane containing both nuclei
- Resemble a p-orbital
Degenerate orbitals
The orbitals that arise from side-on interactions of p orbitals have the same energy
