Chemistry » Essential Ideas in Chemistry » Electronic Configuration

Aufbau Diagrams

Aufbau Diagrams

An element’s electron configuration can be represented using Aufbau diagrams or energy level diagrams. An Aufbau diagram uses arrows to represent electrons. You can use the following steps to help you to draw an Aufbau diagram:

  1. Determine the number of electrons that the atom has.

  2. Fill the s orbital in the first energy level (the 1s orbital) with the first two electrons.

  3. Fill the s orbital in the second energy level (the 2s orbital) with the second two electrons.

  4. Put one electron in each of the three p orbitals in the second energy level (the 2p orbitals) and then if there are still electrons remaining, go back and place a second electron in each of the 2p orbitals to complete the electron pairs.

  5. Carry on in this way through each of the successive energy levels until all the electrons have been drawn.

You can think of Aufbau diagrams as being similar to people getting on a bus or a train. People will first sit in empty seats with empty seats between them and the other people (unless they know the people and then they will sit next to them). This is the lowest energy. When all the seats are filled like this, any more people that get on will be forced to sit next to someone. This is higher in energy. As the bus or train fills even more the people have to stand to fit on. This is the highest energy.

Did You Know?

Aufbau is the German word for “building up”. Scientists used this term since this is exactly what we are doing when we work out electron configuration, we are building up the atoms structure.

Hund’s Rule and Pauli’s Principle

Sometimes people refer to Hund’s rule for electron configuration. This rule simply says that electrons would rather be in a subshell on their own than share a subshell. This is why when you are filling the subshells you put one electron in each subshell and then go back and fill the subshell, before moving onto the next energy level.

Pauli’s exclusion principle simply states that electrons have a property known as spin and that two electrons in a subshell will not spin the same way. This is why we draw electrons as one arrow pointing up and one arrow pointing down.

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