[Itika]

Hey,

this question is giving me quite the trouble. "Which of the ions or atom 1) to 4) has the smallest radius? 1) F^- 2) Ne 3) Na⁺ 4)Mg²⁺"

My chemistry teacher hasn't touched the topic of atomic and ionic radii yet and it doesn't look like he will, so I started researching about it. Seems like it's much easier to compare the radii between atoms and radii between ions, but I haven't got a single clue of how to compare ionic to atomic radii.

Any help is really appreciated!

[sjb]

Hey,

this question is giving me quite the trouble. "Which of the ions or atom 1) to 4) has the smallest radius? 1) F^- 2) Ne 3) Na⁺ 4)Mg²⁺"

My chemistry teacher hasn't touched the topic of atomic and ionic radii yet and it doesn't look like he will, so I started researching about it. Seems like it's much easier to compare the radii between atoms and radii between ions, but I haven't got a single clue of how to compare ionic to atomic radii.

Any help is really appreciated!

Have you learnt about the Bohr model, yet?

[Borek]

Hint: count electrons in each.

[Itika]

Have you learnt about the Bohr model, yet?

Yes, I have. I might have figured it out after thinking for a while. Although the 3 ions and the atom have the same number of electrons, Mg²⁺ has a larger number of protons, which results in a stronger attraction of the shell and in a smaller radius. Could it be the case?

[Borek]

Yes, they are isoelectronic and the only thing that differs is the nucleus charge - the higher the charge, the lower the radius.

[Andy_Ruan]

1) F- 2) Ne 3) Na+ 4)Mg2+

For something like this, you need to realize that all these species have 10 electrons (the same).
The two biggest factors affecting atomic radius are the # electrons, and the effective nuclear charge on
the valence electrons.

In this case, since you know the # electrons are exactly the same, you can only rely on the effective
nuclear charge aka. how much the nucleus attract the electrons. 
In this case, F has 9 protons, Ne has 10p+, Na has 11p+, and Mg has 12p+.
Mg would have the smaller atomic radius since it has the most protons, and thus, would be able to
attract the 10 electrons much closer than any other atom.

[mikasaur]

Andy_Ruan, thanks for providing a good explanation, but please refrain from giving exact answers in your responses. This forum is about providing people with the means to learn and understand, and they can't do that if we just give them the answers to their questions, even if those answers come with good explanations.

This is one of our forum rules you can read about here.

Hmmm, perhaps I spoke too soon. It looks like Itika made an attempt at an answer by suggesting Mg²⁺ had the smallest radius. Your further explanation may be fine and in accordance with the rules. I'll let the mods weigh in, if weighing in is needed.