Atomic vs Ionic Radius

[IsabelMurillo3K]

Throughout the Sapling homework this week, I noticed that several questions asked me to rearrange different elements off of their atomic or ionic radius. I was wondering what is the difference between both the ionic and atomic radius, and how I could identify each? Thanks in advance!

[Eva Becker]

Though seemingly similar, there is a distinction between the atomic and ionic radii. Atomic radius refers to the distance from the nucleus to the normal valence electrons of an atom. Ionic radius, however, refers to the distance from the nucleus to the outermost electrons. For example, the atomic radius of Na is larger than the ionic radius of Na+ because the distance from the nucleus to the outermost electron of a Na+ ion is smaller due to the lack of the 1 valence electron that would have been present in the neutral state of Na. Hope this helped!

[Hasmik Dis 2F]

Also, I wanted to add to Eva's answer the fact that Na+ has a stronger positive nuclear charge than Na. Therefore, that stronger pull the nucleus has on the electrons can account for the smaller radius.

[Gustavo_Chavez_1K]

Honestly, atomic and ionic radii are pretty similar in what they measure. The main and essentially only difference is that the ionic radius measures the distance from the nucleus to the outermost electrons in a ion while the atomic radius measures the distance from the nucleus to the normal valence electrons. For example, the atomic radius of K would be what is considered the measurement of the distance from the nucleus to the "normal" valence electrons. But if we measure a K+ ion, then we would measure the ionic radius. K+ would have a smaller radius since it has a stronger nuclear charge than K and therefore pulls on the electrons more.