Largest atomic radius

[flin5845]

Which of the following would have the greatest atomic radius?

A. Ca2+
B. F-
C. Ar
D. O2-
E. He

I thought the answer was O2- because when you add electrons the nucleus does not have as tight of a attraction to all the electrons, therefore making the radius bigger?

My Kaplan teacher said it is Ar, because O2- would have the electron configuration of Ne...and Ar is bigger than Ne.

But I think that O2- would have 2 less protons than Ne so it is not really the same size as Ne, and should be a little bigger.

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[bharat008]

Which of the following would have the greatest atomic radius?

A. Ca2+
B. F-
C. Ar
D. O2-
E. He

I thought the answer was O2- because when you add electrons the nucleus does not have as tight of a attraction to all the electrons, therefore making the radius bigger?

My Kaplan teacher said it is Ar, because O2- would have the electron configuration of Ne...and Ar is bigger than Ne.

But I think that O2- would have 2 less protons than Ne so it is not really the same size as Ne, and should be a little bigger.

Is it Argon??

 

[AlbinoPolarBear]

Which of the following would have the greatest atomic radius?

A. Ca2+ (3rd row)
B. F- (2nd row)
C. Ar (3rd row)
D. O2- (2nd row)
E. He (1st row)

I thought the answer was O2- because when you add electrons the nucleus does not have as tight of a attraction to all the electrons, therefore making the radius bigger?

The radius of an atom increase as we go down the periodic table, as more shells will mean electrons are farther from nucleus.

Radius will decrease as we go from left to right in the periodic table, because of 'effective nuclear charge', which means if we add 1 proton and 1 electron, that proton will 'have more power' and pull that and other electrons closer to the nucleus.

So let's look at the answer choices.
Which row are valence shell electrons in, after we accounted for the charges?

A. Ca2+ (3rd row)
B. F- (2nd row)
C. Ar (3rd row)
D. O2- (2nd row)
E. He (1st row)

So it's between Ca2+ and Ar, because the valence electrons are in 3rd row.

Ca2+ has 20 protons and 18 electrons, while Ar has 18 protons and 18 electrons.

The 2 extra protons of the Ca2+ will pull the electrons closer to the nucleus, making it smaller. Therefore, Ar will be bigger.

 

[indigenoustw]

Which of the following would have the greatest atomic radius?

A. Ca2+
B. F-
C. Ar
D. O2-
E. He

I thought the answer was O2- because when you add electrons the nucleus does not have as tight of a attraction to all the electrons, therefore making the radius bigger?

My Kaplan teacher said it is Ar, because O2- would have the electron configuration of Ne...and Ar is bigger than Ne.

But I think that O2- would have 2 less protons than Ne so it is not really the same size as Ne, and should be a little bigger.

I would have eliminated He, F-, and O2- before even thinking about it because these three would have an electron configuration of Ne, like you said. And then Ca2+ have more protons than Ar so probably a tighter attraction for the electrons => smaller atomic radius, so Ar would have bigger atomic radius than Ca2+.

I don't know about your argument, but protons and electrons attract; if you have more electrons, would it make sense if they repel even more? I don't think so. Someone with a better chemistry background can answer this, but I think the answer should be Ar.

 

[FROGGBUSTER]

O2- is bigger than Ne, but Ar is way bigger than either of them because you're adding subshells as you go down the periodic table.

 

[AlbinoPolarBear]

O2- is bigger than Ne, but Ar is way bigger than either of them because you're adding subshells as you go down the periodic table.

Shells

 

[FROGGBUSTER]

Shells

well if you're adding shells, you're adding subshells. 🙂

 

[AlbinoPolarBear]

well if you're adding shells, you're adding subshells. 🙂

Didn't want the OP to be confused with adding subshells across the periodic table, because adding subshells while still in the same shell will decrease the atomic radius because of effective nuclear charge.

 

[LetsGo2DSchool]

Da Bear is correct. Ca2+ and Ar are isoelectronic species so by focusing on the effective nuclear charge, you can conclude that Ar will be bigger.

 

[spoog74]

Da Bear is correct. Ca2+ and Ar are isoelectronic species so by focusing on the effective nuclear charge, you can conclude that Ar will be bigger.

nvm the answer is Ag

 

[EpicDentist]

nvm the answer is Ag

Ar *

 

[RING12]

Which of the following would have the greatest atomic radius?

A. Ca2+
B. F-
C. Ar
D. O2-
E. He

I thought the answer was O2- because when you add electrons the nucleus does not have as tight of a attraction to all the electrons, therefore making the radius bigger?

My Kaplan teacher said it is Ar, because O2- would have the electron configuration of Ne...and Ar is bigger than Ne.

But I think that O2- would have 2 less protons than Ne so it is not really the same size as Ne, and should be a little bigger.

in this case you should look at the trends in periodic table. from left to right the atomic radius decrease, and from top to bottom (group) atomic radius increase. If you look this way you would get Ar as answer.

 

[yappy]

OP - your thinking was correct if this was an isoelectric series. Becaues it is not you need to look at the placement of each atom on the table. As others have stated atoms get larger when going right to left and from top to down of the table.

But an anion is always larger than its neutral species and a cation is always smaller than its neutral species.