list show obvious patterns. In particular, every set of five elements (in ) before each noble gas (group 18, in ) heavier than helium have successive numbers of electrons in the outermost shell, namely three to seven. Sorting the table by chemical group shows additional patterns, especially with respect to the last two outermost shells. (Elements 57 to 71 belong to the lanthanides, while 89 to 103 are the actinides.) The list below is primarily consistent with the Aufbau principle. However, there are a number of exceptions to the rule; for example palladium (atomic number 46) has no electrons in the fifth shell, unlike other atoms with lower atomic number. The elements past 108 have such short half-lives that their electron configurations have not yet been measured, and so predictions have been inserted instead. See also Periodic table (electron configurations) Electron counting 18-electron rule Core charge References Electron Atomic physics Quantum mechanics Chemical bonding