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

1 Answer
Dec 2, 2015

This element is phosphorus and it has five valence electrons.


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: #"1s"^2"2s"^2"2p"^6"3s"^2"3p"^3"#. The highest energy (outermost) #"s"# and #"p"# sublevels make up the valence shell. So according to the electron configuration, there are #5# electrons in the valence shell.