Chemistry Practice Problems
Periodic Trend: Monoatomic ions and electron configuration
Questions:
1. Write the ground state electron configuration of two anions and two cations that
are isoelectronic with argon.
2. Write the ground state electron configuration of Ni2+ and Sn3+. Is either ion
isoelectronic with a noble gas? If so, which noble gas?
Answers:
1. Isoelectronic ions will have the same electron configuration as argon:
1s22s22p63s23p6 or simply [Ar]. K+, Ca2+, S2–, and Cl– all have this electron
configuration.
2. First write the electron configuration of the metal atom then remove the electrons
from the subshell with the highest n value, p-orbital electronsbefore s-orbital
electrons.
Ni: [Ar]4s23d8
Ni2+: [Ar]3s8
Sn: [Kr]5s24d105p1 Sn3+: [Ar]4d10
Neither ion is isoelectronic with a noble gas.