Electron Configuration - Aufbau Principle and Madelung Rule - Other Exceptions To Madelung's Rule

Other Exceptions To Madelung's Rule

There are several more exceptions to Madelung's rule among the heavier elements, and it is more and more difficult to resort to simple explanations such as the stability of half-filled subshells. It is possible to predict most of the exceptions by Hartree–Fock calculations, which are an approximate method for taking account of the effect of the other electrons on orbital energies. For the heavier elements, it is also necessary to take account of the effects of Special Relativity on the energies of the atomic orbitals, as the inner-shell electrons are moving at speeds approaching the speed of light. In general, these relativistic effects tend to decrease the energy of the s-orbitals in relation to the other atomic orbitals.

Electron shells filled in violation of Madelung's rule (red)
Period 4 Period 5 Period 6 Period 7
Element Z Electron Configuration Element Z Electron Configuration Element Z Electron Configuration Element Z Electron Configuration
Lanthanum 57 6s2 5d1 Actinium 89 7s2 6d1
Cerium 58 6s2 4f1 5d1 Thorium 90 7s2 6d2
Praseodymium 59 6s2 4f3 Protactinium 91 7s2 5f2 6d1
Neodymium 60 6s2 4f4 Uranium 92 7s2 5f3 6d1
Promethium 61 6s2 4f5 Neptunium 93 7s2 5f4 6d1
Samarium 62 6s2 4f6 Plutonium 94 7s2 5f6
Europium 63 6s2 4f7 Americium 95 7s2 5f7
Gadolinium 64 6s2 4f7 5d1 Curium 96 7s2 5f7 6d1
Terbium 65 6s2 4f9 Berkelium 97 7s2 5f9
Scandium 21 4s2 3d1 Yttrium 39 5s2 4d1 Lutetium 71 6s2 4f14 5d1 Lawrencium 103 7s2 5f14 7p1
Titanium 22 4s2 3d2 Zirconium 40 5s2 4d2 Hafnium 72 6s2 4f14 5d2 Rutherfordium 104 7s2 5f14 6d2
Vanadium 23 4s2 3d3 Niobium 41 5s1 4d4 Tantalum 73 6s2 4f14 5d3
Chromium 24 4s1 3d5 Molybdenum 42 5s1 4d5 Tungsten 74 6s2 4f14 5d4
Manganese 25 4s2 3d5 Technetium 43 5s2 4d5 Rhenium 75 6s2 4f14 5d5
Iron 26 4s2 3d6 Ruthenium 44 5s1 4d7 Osmium 76 6s2 4f14 5d6
Cobalt 27 4s2 3d7 Rhodium 45 5s1 4d8 Iridium 77 6s2 4f14 5d7
Nickel 28 4s2 3d8 or
4s1 3d9 (disputed)
Palladium 46 4d10 Platinum 78 6s1 4f14 5d9
Copper 29 4s1 3d10 Silver 47 5s1 4d10 Gold 79 6s1 4f14 5d10
Zinc 30 4s2 3d10 Cadmium 48 5s2 4d10 Mercury 80 6s2 4f14 5d10

The electron-shell configuration of elements beyond rutherfordium is not yet known, but they are expected to follow Madelung's rule without exceptions until element 120.

Read more about this topic:  Electron Configuration, Aufbau Principle and Madelung Rule

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