what is abnormal about phosphoruss valence shell? justify phosphoruss valence shell structure.

Brief Explanations:

Phosphorus (P) has an atomic number of 15, so its electron configuration is $1s^2 2s^2 2p^6 3s^2 3p^3$. The valence shell is the outermost shell (n = 3 here), containing $3s^2 3p^3$ (5 electrons). Normally, for main - group elements, the octet rule (8 valence electrons for stability) is common, but phosphorus can expand its valence shell. It has empty 3d orbitals, so it can accommodate more than 8 electrons in its valence shell (e.g., in compounds like $PCl_5$, where P has 10 valence electrons, using one 3s, three 3p, and one 3d orbital for hybridization). This ability to expand the valence shell (exceed the octet) is “abnormal” compared to elements without accessible d - orbitals in their valence shell (like second - period elements). The justification is based on its electron configuration: the presence of empty 3d orbitals in the n = 3 shell allows phosphorus to use these orbitals for bonding, enabling it to have more than 8 valence electrons when forming compounds, as the 3d orbitals are close in energy to 3s and 3p, so they can participate in hybridization and bonding.

Answer:

Phosphorus can expand its valence shell (accommodate > 8 electrons) because it has empty 3d orbitals (electron config: $1s^2 2s^2 2p^6 3s^2 3p^3$; valence shell n = 3 has 3d orbitals). In compounds (e.g., $PCl_5$), it uses 3d orbitals to have 10 valence electrons, unlike elements without accessible d - orbitals (e.g., second - period elements) that follow the octet rule strictly.