Science, Tech, Math › Science Madelung's Rule Definition What Is Madelung's Rule in Chemistry? Share Flipboard Email Print Madelung's Rule is used to fill electron orbitals. Todd Helmenstine Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated February 15, 2018 Madelung's Rule Definition Madelung's rule describes electron configuration and the filling of atomic orbitals. The rule states: (1) Energy increases with increasing n + l (2) For identical values of n + l, energy increases with increasing n The following order for filling orbitals results: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s) The orbitals listed in parentheses are not occupied in the ground state of the heaviest atom known, Z = 118. The reason orbitals fill this way is because the inner electrons shield the nuclear charge. Orbital penetration is as follows:s > p > d >f Madelung's rule or Klechkowski's rule originally was described by Charles Janet in 1929 and rediscovered by Erwin Madelung in 1936. V.M. Klechkowski described the theoretical explanation of Madelung's rule. The modern Aufbau principle is based on Madelung's rule. Also Known As: Klechkowski's rule, Klechowsy rule, diagonal rule, Janet rule Exceptions to Madelung's Rule Keep in mind, Madelung's rule may only be applied to neutral atoms in the ground state. Even then, there are exceptions from the ordering predicted by the rule and experimental data. For examples, the observed electron configurations of copper, chromium, and palladium are different from predictions. The rule predicts the configuration of 9Cu to be 1s22s22p63s2 3p64s23d9 or [Ar]4s23d9 while the experimental configuration of a copper atom is [Ar]4s13d10. Filling the 3d orbital completely gives the copper atom a more stable configuration or lower energy state.