Atomic physics


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Noble gases electron configuration
The chemical inertness of noble gases is due to the fact that for those elements the last s-shell and p-shell, constituting the valence shells which contain eight electrons, are fully occupied. The whole electron configuration acts as a fortress, locking all their electrons in, blocking the exhange of electrons or the sharing of electrons with other elements. Chemical reactions with other elements are therefore virtually ruled out.

For the principle quantum number n=1 there is no p-shell, there is only one s-shell. Therefore in the case of helium, with atomic number 2, only the s-shell is fully occupied which is sufficient to have the two electrons act as a fortress for such a small atom.

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Electron configuration of chemical reactive elements
All the reactive elements listed above have a single electron in their s-shell just outside their outer fully ocupied p-shell (or s-shell in the case of He). It is like having a single electron just outside the fortress, just waiting to be snatched. These elements are in fact eager to donate one electron in a chemical process with electron hungry elements to form ionic bonds. text


Extended electron configuration template
The most heaviest naturally occuring element is 92Uranium with a mass number of 238. It has a half lifetime of 4.4 billion years. Above that atomic number of 92 the half lifetime decrases with increasing atomic number. Many of these heavy elements are made synthetically. The synthetic element 118Organesson (mass number 294) has a half lifetime of 0.69 seconds.
So this template will not be used for n+ℓ values above 8 and is actually shown for educational purposes to illustrate the methodology of the Madelung Aufbau principle. However those higher orbital states might be relevant for heavy atoms in an excited state.

Limitations of Madelung's Aufbau principle
Furthermore it must be noted that theoretical calculation have learned that for for elements with atomic number higher than 120 the way at which the higher orbitals are filled will deviate from Madelung's Aufbau principle as a result of overlapping orbitals due to the increasing influence of relativistic effects.
Observations have led to the conclusions that speed is a physical property which has to be assigned to all the electrons each in their own quantum state around an atom nucleus. This speed appears to be a fraction of the lightspeed which can not be neglected and also appears to be increasing with increasing principle quantum number. This relativistic speed of the electrons has impact on the total mass of the electrons and therefore impact on their quantum states. It can be illustrated that in the mathematical wavefunctions, describing the quantum states of the electrons, we have to incorporate these electron mass increases due to relativistic effects to explain the observed perturbations in the orbitals.

It is interesting to know that these relativistic effects can affect the optical properties of matter at a macroscopic scale. For example, 79Au (gold) should have a silvery like appearance like most other metals according to non-relativistic quantum mechanics. But gold has a somewhat yellowish appearance which can be explained with relativistic quantum mechanics.

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Types of bonds between atoms
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