Ionization Energy (5) Orbitals and the Pauli Exclusion Principle

Ionization energy (5) Orbitals and the Pauli Exclusion Principle.

Before I finish posting on ionisation energy and related areas I thought I ought to discuss atomic orbitals. 

What have atomic orbitals to do with ionisation energy?

Let’s go back to the way we can represent the electron configuration of an atom using the electrons in boxes approach.

Here is how sodium’s electron configuration is represented:

The question we want to ask is what do the boxes represent and why are the three boxes in the 2p subshell labelled p_x, p_y and p_z?

The box represents an atomic orbital.

Atomic orbitals contain a maximum of two electrons. 

These electrons spin in opposite directions.

The Pauli exclusion principle dictates that each electron in an atom has to have an exclusive quantum number i.e. a unique identifier.

The attribution of opposite spins facilitates that unique identity.

For example each 2s electron is unique because they have opposite spins.

So how can each of the 2p electrons be unique?

The answer lies in the distribution of the electrons around the atom.

The shape of the atomic orbitals shows how the electrons are distributed around the atom.

The best place on the net to investigate atomic orbitals is here at the Orbitron.

For s orbitals that pattern of the distribution of electrons is spherical.

But p orbitals are not spherical but essentially dumbbell shaped.

As you can see the distribution is symmetrical about the 3D axis. 

Another way of thinking about the orbital is to realise it is a space in the atom where there is a 95% probability of finding the electron. 

The space is the result of calculations using the electron’s wave function ψ in the Schrodinger wave equation.

Plotting the square of the wave function ψ² against r the distance from the nucleus generates the different orbital shapes. 

If we extend our description of the shapes of atomic orbitals to the d subshell then there are 5 and each has a unique position in space around the nucleus. 

What these models of electron subshells do is to de bunk the idea that atoms are spherical in shape. 

Studies of atomic orbitals are important when we discuss the bonding in organic molecules (see here) and transition metal complexes. 

You can see more about Schodinger’s Cat here