BC.04 Atomic and molecular orbitals

What is a wave function?

A wave function (Ψ) is a function that relates the location of an electron at a given point in space (x, y, and z coordinates) to the amplitude of its wave, which corresponds to its energy.

What is electron density (Ψ^2)?

It is the probability of finding an electron at a point, which leads to a distribution of probabilities in space.

Draw a graph of wave function, electron density and radial electron distribution for a 1s orbital. Note the most likely distance to find an electron on the radial electron distribution graph.

What is the most likely distance to find an electron in a 2s orbital?

2Å

What is Coulomb’s Law?

Where q is charge and r is separation distance.

What is the Aufbau principle?

Electrons placed in orbitals starting with lowest energy and working up

What is the Pauli exclusion principle?

Two electrons per orbital, spins paired

What is Hund’s rule?

When multiple orbitals of same energy are available, electrons are distributed among them, spins parallel

When the electrons are in phase, a ??? forms. This is an energetically favourable interaction.

Bonding orbital (σ)

When the electrons are **not** in phase, a ??? forms. This is an energetically unfavourable interaction (in fact more unfavourable than if the electrons were just separate from each other).

Anti-bonding orbital (σ\*)

Why doesn’t Helium exist as a diatomic molecule?

Because 2 electrons exist in both bonding and anti-bond orbitals, which is unfavourable to form.