How To Write Electron Configurations Examples . 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p. If you know the element, look on the periodic table to find the atomic number. Electron Configuration of Transition Metals Chemistry LibreTexts from chem.libretexts.org There is a shorthand way of writing electron configurations. Electron configurations for the second period. That number must be the same as proton number.