Textbook Question 1F.3

[Nina Fukui 2J]

1F.3 Place the following ions in order of increasing ionic radius: S2-, Cl-, P3-.
How would I do this?

[Madilyn Schindler 3E]

P3- is the largest ion followed by S2- and Cl-. This is because P has the least number of protons and Cl has the greatest number of protons. They all have the same number of electrons, but as the number of protons decreases, the strength of attraction between the positively charged protons and the negatively charged electrons decreases as well. This allows the electrons to be farther away and therefore the ion to be larger.

[Maaria Abdel-Moneim 2G]

In order from largest to smallest it would be P3-, S2-, P-. The atomic radius decreases as you go across a period so P is bigger in the first place. You are adding three electrons to P making it even larger than it was before. The same trend happens for S2- and P-

[George_Yin_3I]

These three anions are isoelectronic; in this case, the greater the proton number, the smaller the ionic radius is.

[George_Yin_3I]

It is the same logic with cations. For example, the ionic radius of Ca2+ is smaller than K+, given that both of them contain 18 electrons.