Why we dont write down the subshells to? I hope the question is not to much non specific. Thanx for answers.
This is a good question, and the answer has to do with energy. First, to clarify nomenclature, we'll refer to the four quantum numbers: the principle quantum number (aka energy level, 1, 2, 3, etc.), the azimuthal quantum number (s, p, d, f, etc.), the magnetic quantum number (e.g. which specific type of orbital such as px
), and the spin quantum number (+1/2 or -1/2). The energy of an orbital depends on the principle quantum number and (for all atoms except atoms with only one electron) the azimuthal quantum number. In most cases, the magnetic quantum number and spin quantum number have no effect on the energy of the orbital (there are, howerver, special cases, where states with different magnetic or spin quantum numbers have different energies--for example, the presence of an external magnetic field).
Because states with different azimuthal quantum number have the same energy, the order in which the orbitals are filled does not matter. So, for an atom like boron (electron configuration 1s2
), the highest energy electron could have gone into either the px
orbital because they all have equal energy. Since we don't know which orbital the electron went into, we cannot provide the information in the electron configuration.