Question: how many valence electrons are in an atom of phosphorus express your answer numerically?
Answer: there are 15 electrons in total, there must be 5 electrons at the third energy level. there are 3 energy levels, so the electrons at the third are outer, or valence, electrons. this means that there are 5 valence electrons. all neutral atoms of the elements in group 5 have 5 valence electrons.