Question

Arrange the following atoms or ions in order of decreasing ionization energy:

K⁺, Cl^-, S^2-, Ca²⁺

^{Please show how you get the answer. I am confused because all of the ions would be like the nearest noble gas. So wouldn't all of them have the same ioniation energy?}

Answer 1

K⁺=1.33, Ca⁺²=0.99, Cl^-=1.81, S^-2=1.84

Isoelectronic species means same number of electron but different mass number.Electrons in the electron cloud are constantly repelling each other and the more electrons the larger the shell. Since all of these atoms have the same number of electrons, the only thing that changes are the number of protons.

As nuclear charge increases in an isoelectronic series the ions become smaller

As we move across a period, Zeff increases. Therefore, it becomes more difficult to remove an electron.

if you observe they are close atomic numbers S (16), Cl (17), K (19), and Ca (20) , Arrange the ions K+, Cl –, Ca2+, and S2– in order of DECREASING size. These form an isoelectronic series of ions Size decreases as the nuclear charge of the ion increases. The atomic numbers of the ions are S (16), Cl (17), K (19), and Ca (20)

if we are starting ions as indicated then note they are all isoelectronic Ar. - thus the one with themost protons will have greatest ionication energy

S -2 < Cl- < K+ < Ca+2