Here's why:
* Valence Electrons: Valence electrons are the electrons in the outermost shell of an atom, which are involved in chemical bonding.
* Phosphorus (P): Phosphorus is in group 15 of the periodic table and has the electron configuration [Ne] 3s² 3p³. This means it has 5 valence electrons (2 in the 3s orbital and 3 in the 3p orbitals).
* Arsenic (As): Arsenic is also in group 15 and has the electron configuration [Ar] 4s² 4p³. It also has 5 valence electrons.
Since both elements have the same number of valence electrons in the same orbitals, they share the same valence electron configuration. This is why elements in the same group of the periodic table tend to have similar chemical properties.
