Electron Configurations in Multielectron Atoms

In addition to the conditions for the electronic structures of multielectron atoms established by the monoelectronic wave functions and their relative energies mentioned above, other restrictions should also be considered. One of them is the Pauli principle stating that no two electrons can have the same quantum numbers. Thus one orbital can contain a maximum of two electrons provided they have different spin quantum numbers. Other practical rules or restrictions refer to the influence of interelectronic interactions on the electronic structures established by Hund s rules. The electrons with the same n and / values will occupy first orbitals with different nti and the same rris (paired spins). 

The aufbau principle is used to build up the electronic structures of multielectron atoms by adding protons and electrons to the hydrogen atom. According to this principle electrons are placed in hydrogen-like orbitals filling them in the order of decreasing stability (energy of the orbital and interelectronic 

The Periodic Table constitutes the best representation of the properties of the elements where the tight relationship between their chemical and electronic properties is clearly stated. A version of the Periodic Table with group enumeration as recently accepted by lUPAC is reproduced in Fig. 1.7. 

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