This is a worked example problem showing the steps necessary to determine the electron configuration of an element using the principles learned in the previous sections
Determine the electron configuration of silicon.
Silicon is element 14. It has 14 protons and 14 electrons. The lowest energy level of an atom is filled first. The arrows in the graphic show the s quantum numbers, spin 'up' and spin 'down'.
Step A shows the first two electrons filling the 1s orbital and leaving 12 electrons.
Step B shows the next two electrons filling the 2s orbital leaving 10 electrons.
The 2p orbital is the next available energy level and can hold six electrons. Step C shows these six electrons and leaves us with four electrons.
Step D fills the next lowest energy level, 3s with two electrons.
Step E shows the remaining two electrons starting to fill the 3p orbital. Remember one of the rules of the aufbau principle is that the orbitals are filled by one type of spin before the opposite spin starts to appear. In this case, the two spin up electrons are placed in the first two empty slots, but the actual order is arbitrary. It could have been the second and third slot or the first and third.
The electron configuration of silicon is 1s22s2p63s23p2.