How many valence electrons are in an atom of phosphorus?

1 Answer
Apr 11, 2018

Answer:

#5#

Explanation:

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.