isotope              p⁺              n⁰              e^-              electron locations               valence electrons             dot diagram

                                                                                                                                                                                              4p ___ ___ ___

                                                                                                                                                                                              3d ___ ___ ___ ___ ___

                                                                                                                                                                                               4s ___

                                                                                                                                                                                               3p ___ ___ ___

                                                                                                                                                                                               3s ___

                                                                                                                                                                                               2p ___ ___ ___

                                                                                                                                                                                               2s ___

                                                                                                                                                                                               1s ___