1. Aufbau Principle:
* Electrons fill orbitals in order of increasing energy levels.
* The order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, ...
2. Hund's Rule:
* Electrons fill orbitals individually before doubling up in the same orbital.
* Each orbital within a subshell gets one electron before any orbital gets two electrons.
3. Pauli Exclusion Principle:
* No two electrons in an atom can have the same set of four quantum numbers.
* Each orbital can hold a maximum of two electrons with opposite spins.
Electronic Configuration:
1. 1s²: The first shell (n=1) has one subshell (s) that holds 2 electrons.
2. 2s²: The second shell (n=2) has an s subshell that holds 2 electrons.
3. 2p⁶: The second shell (n=2) also has a p subshell that holds 6 electrons.
4. 3s²: The third shell (n=3) has an s subshell that holds 2 electrons.
5. 3p⁶: The third shell (n=3) also has a p subshell that holds 6 electrons.
6. 4s²: The fourth shell (n=4) has an s subshell that holds 2 electrons.
7. 3d⁶: The third shell (n=3) also has a d subshell that holds 10 electrons. It has 6 electrons in this case.
Therefore, the full electronic configuration of iron (Fe) is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
Or in a more compact form:
[Ar] 4s² 3d⁶ (where [Ar] represents the electronic configuration of Argon, which is the noble gas preceding iron)
