How many valence electrons are in an atom of phosphorus?

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Answer 1 · 2018-04-11T16:22:51

#5#

phosphorus has atomic number #15#, and is in group #5# and period #3# of the Periodic Table.

it is in period #3#, because it has orbits at #3# energy levels.

there are #2# electrons at the first energy level, and #8# at the second energy level.

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.