Cation vs Anion Size [ENDORSED]

[Catherine Trinh 3K]

I know that cations are smaller than their parent atoms, while anions are larger. What is the reason for this? Does it have to do with the positive and negative charges of each one?

[Annie Chang 3G]

Cations are ions with a net positive charge due to the loss of one or more valence electrons. The removal of an electron would vacate the valence shell and decrease the total electron-electron repulsion resulting in a smaller electron cloud. There is also a greater attraction of the electrons to the nucleus as there is a fewer number of electrons while the nuclear charge remains the same.

\Anions, on the other hand, are ions with a net negative charge due to the addition of one or more valence electrons. The addition of an electron increases electron-electron repulsion causing the electrons to spread out more and make the electron cloud expand.

[Tyler_Honrada_1L]

For different anions, how would we determine what one is bigger/smaller especially when they're so close to each other on the periodic table?

[Sonja Kobayashi 1H]

Hello!
To determine which anion is bigger, refer to the atomic radii trends for the parent ions on the periodic table. Therefore, the atomic radius and therefore the anion size will increase down a family and increase across a row! Remember that anions are larger than the parent ion however by looking at the parent ions, you can compare the sizes!