Aufbau Principle
The physical and chemical properties of elements is determined by the atomic structure. The atomic structure is, in turn, determined by the electrons and which shells, subshells and orbitals they reside in. The rules af placing electrons within shells is known as the Aufbau principle. These rules are:
1. Electrons are placed in the lowest energetically available subshell.
2. An orbital can hold at most 2 electrons.
3. If two or more energetically equivalent orbitals are available (e.g., p, d etc.) then electrons should be spread out before they are paired up (Hund's rule).
In an orbital, electrons will fill all available positions of the same value of s before the opposite spin value appears.
No two electrons in an atom can have identical quantum numbers. This is an example of a general principle which applies not only to electrons but also to other particles of half-integer spin (fermions). It does not apply to particles of integer spin (bosons).
1. Electrons are placed in the lowest energetically available subshell.
2. An orbital can hold at most 2 electrons.
3. If two or more energetically equivalent orbitals are available (e.g., p, d etc.) then electrons should be spread out before they are paired up (Hund's rule).
Hund's rule
In an orbital, electrons will fill all available positions of the same value of s before the opposite spin value appears.
Pauli's Exclusion
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