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

Dec 2, 2015

Answer:

This element is phosphorus and it has five valence electrons.

Explanation:

We can determine this two ways. The element with 15 protons, meaning it has atomic number 15, is phosphorus. Phosphorus is in group 15/VA. Based on its group number, phosphorus has 5 valence electrons, as do all of the elements in that group.

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.