The half-filled orbital rule generally only works with transition metals and the filling of d (from n-1) vs. s (from n), where n is principal quantum number. The reason is more quantum mechanical in nature and beyond the scope of most general chemistry courses but in short, the d (n-1) orbitals are very close in energy to the s 👎 orbitals in energy if you do the calculation and so you get a little added stabilization from half-full d orbitals that lower them slightly. This slight lowering is enough to lower the d (n-1) orbital below the s 👎. It is not enough to lower p below s for the same n shell.