Write electron configurations for these atoms and ions, and comment on the result.

a.) Ar

b.) Cl-

c.) S2-

d.) P3-

A) Ar, Z = 18 = > 18 electrons = > 1s2 2s2 2p6 3s2 3p6

b) Cl-

Cl, Z = 17 = > Cl - = 17e + 1e = 18 electrons = > same electron configuration as Ar

c) S2-

S, Z = 16 = > S (2-) = 16e + 2e = 18 electrons = > same electron configuration as Ar

d) P (3-), Z = 15 = > P (3-) = 15e + 3e = 18 electrons = > same electron configuration as Ar

Cl - ion has one more electron than Cl atom, S2 - ion has two more electrons than S atom, and P3 - has three more electrons than P atom.

Then the three ions have 18 electrons, which is the number electrons of Ar atoms, and therefore the 4 species have the same electron configuration of Ar.