Comparing sizes of atoms

[deleted647690]

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Looking at F-, Ne, and Na+

They all have the same number of electrons, but TBR says that Na+ is the smallest because it has the greatest nuclear charge. Are they referring to Z effective? Wouldn't F hold electrons most tightly and thus be the smallest?

 

[freak7]

From Wiki:

"Ions may be larger or smaller than the neutral atom, depending on the ion's electric charge. When an atom loses an electron to form a cation, the other electrons are more attracted to the nucleus, and the radius of the ion gets smaller. Similarly, when an electron is added to an atom, forming an anion, the added electron increases the size of the electron cloud by interelectronic repulsion."

Are they referring to Z effective?

No, they're referring to Z.

Wouldn't F hold electrons most tightly?

F would yes, but F- would not. Think about it, if I add an electron and create a negative charge, the electrons would want to push away from each other. You may be conflating F's high electronegativity with how it affects F-'s size.

This picture sums it up well, (also from Wiki):

Caption: "Relative radii of atoms and ions. The neutral atoms are colored gray, cations red, and anions blue."

 

[rabbott1971]

Point is, they have the same number of electrons, but different numbers of protons. The one with the most protons will have the smallest radius, because the extra proton(s) attracts the electrons in more tightly. Fluorine's high electronegativity I believe applies more to how it draws in electrons when it is in a bonding relationship, less so as to when you're thinking just about atomic radius.