# What are some common mistakes students make with electron configurations?

Getting the energy levels (the subshells) in the wrong order - especially when $d$-orbitals come into play. Forgetting how many electrons can populate each subshell. Even getting the number of electrons wrong. These are a few I have encountered.
Students have difficulty understanding why 4$s$ orbitals fill before 3$d$ orbitals and get the order wrong.