Question

in my textbook it is given that 5 valence electrons are preceded by 8 electrons in case of phosphorous....but we know that electronic configuration of P is 1s2 2s2 2p6 3s2 3p3...here we can see that 5 valence electrons are preceded by 10 electrons then in book why it is given as 8

Answer 1

The atomic number of Phosphorus is 15.
Hence,
K shell contains 2 electrons.
L shell contains 8 electrons.
M shell contains 5 electrons.
Electronic configuration= 2,8,5

Thus, 5 valence electrons are preceded by 8 electrons.
Hope you got this!