# How many valence electrons does an ion with 15 protons have?

Another way we can answer this question is to write the electron configuration for a neutral phosphorus atom, which would have 15 electrons: $\text{1s"^2"2s"^2"2p"^6"3s"^2"3p"^3}$. The highest energy (outermost) $\text{s}$ and $\text{p}$ sublevels make up the valence shell. So according to the electron configuration, there are $5$ electrons in the valence shell.