Dat Destroyer Gen Chem Atom Size Question #346

[Mrhyde]

Dat Destroyer Gen Chem Atom Size Question #346


I dont understand this question or the explanation.

To me this explanation would only make sense if this question was discussing an Isoelectronic Series. But we are not Since Al+3 would land us at "Neon" ... but K+ and Ca ++ would be isoelectronic and land both at Argon. In that case then CA++ would be smaller and K+ would be larger...... Thus: K+ > Ca++

But then going back to Al+3 ----- My issue understanding Al+3 placement in this answer is that Al+3 has the least amount of protons and usually if it were ALL isoelectronic (even though we are not in this problem) then the one with the most protons would be the smallest. So carrying over with that thinking I would have thought the answer would be :

Al +3 > K+ > Ca++

Because Aluminum has the LEAST number of protons and this is not an isoeletronic series { because if it were an isoeletroncic series then the answer would listed as correct would make sense to me but it does not make sense to me.

The answer listed as correct is K+> Ca++> Al +3

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[hopefuldentist123]

I think they are referring to isoelectronic in the sense that they have the same valence number of electrons, all of which listed above will have 8 so they all have the same number of valence electrons and can be compared

 

[Mrhyde]

I thought they all had to land on the same element to be isoelectronic ? at least all the examples I have seen have , for Example : K+ , Ca++ , Cl-, S-- would all land on the spot of Argon

 

[DMikes]

Dat Destroyer Gen Chem Atom Size Question #346


I dont understand this question or the explanation.

To me this explanation would only make sense if this question was discussing an Isoelectronic Series. But we are not Since Al+3 would land us at "Neon" ... but K+ and Ca ++ would be isoelectronic and land both at Argon. In that case then CA++ would be smaller and K+ would be larger...... Thus: K+ > Ca++

But then going back to Al+3 ----- My issue understanding Al+3 placement in this answer is that Al+3 has the least amount of protons and usually if it were ALL isoelectronic (even though we are not in this problem) then the one with the most protons would be the smallest. So carrying over with that thinking I would have thought the answer would be :

Al +3 > K+ > Ca++

Because Aluminum has the LEAST number of protons and this is not an isoeletronic series { because if it were an isoeletroncic series then the answer would listed as correct would make sense to me but it does not make sense to me.

The answer listed as correct is K+> Ca++> Al +3

You are over thinking this.

Keep in mind that size INCREASES as you move down a group and DECREASES as you move left to right in a period.

Al 3+ "corresponds" to Neon, which would definitely be smaller than K+ or Ca++ corresponding to Argon.

You have the trend for K+ and Ca++ correct. Just remember the more basic rules.

 

[DAT Destroyer]

Dat Destroyer Gen Chem Atom Size Question #346


I dont understand this question or the explanation.

To me this explanation would only make sense if this question was discussing an Isoelectronic Series. But we are not Since Al+3 would land us at "Neon" ... but K+ and Ca ++ would be isoelectronic and land both at Argon. In that case then CA++ would be smaller and K+ would be larger...... Thus: K+ > Ca++

But then going back to Al+3 ----- My issue understanding Al+3 placement in this answer is that Al+3 has the least amount of protons and usually if it were ALL isoelectronic (even though we are not in this problem) then the one with the most protons would be the smallest. So carrying over with that thinking I would have thought the answer would be :

Al +3 > K+ > Ca++

Because Aluminum has the LEAST number of protons and this is not an isoeletronic series { because if it were an isoeletroncic series then the answer would listed as correct would make sense to me but it does not make sense to me.

The answer listed as correct is K+> Ca++> Al +3

From the literature, we find K+ is 231pm, Ca++ is 197pm, and Al+++ is 143 pm as predicted by the solution to this problem. Yes...they are isoelctronic, since they have the SAME electron configuration.....BUT.....they dont have the same nuclear charge. As electrons are removed, the nucleus will exert a "pull " on the electron cloud........Here is an example.....We expect the Ca+2, with the greatest nuclear charge will have a greatest attraction of its electrons. S2- has the smallest nuclear charge will not have as much pull of its electrons toward the nucleus. Therefore, the ionic size: Ca+2 < K+ < Cl- < S2- (smallest) (largest) As you can see,,,,,,,just because they are isoelectronic does NOT mean they have the same size !!!!

Hope this helps.

Dr. Romano

 

[0rgansm]

Unrelated... but when's your test? I've seen you asking Destroyer questions for what seems like months

 

[Mrhyde]

You are over thinking this.

Keep in mind that size INCREASES as you move down a group and DECREASES as you move left to right in a period.

Al 3+ "corresponds" to Neon, which would definitely be smaller than K+ or Ca++ corresponding to Argon.

You have the trend for K+ and Ca++ correct. Just remember the more basic rules.

lol but relating to what you said then you are contradicting yourself . When you compare Neon to Argon then that would mean Argon is larger then Neon since Argon lies below and thus is lower and size increases as you go down

 

[Mrhyde]

Unrelated... but when's your test? I've seen you asking Destroyer questions for what seems like months

I had not taken Gen Chem in like 2 years and even when I took it I did not understand it and when I took it , I took it at a community college and barley past. So it took me a good amount of time to re-learn it recently on my own and actually try to Completely understand it. So it might look like I have been "studying" for a long time but I personally do not consider me learning something for the first time as studying it, .... So I really have not been studying for a long long time. lol

 

[Mrhyde]

From the literature, we find K+ is 231pm, Ca++ is 197pm, and Al+++ is 143 pm as predicted by the solution to this problem. Yes...they are isoelctronic, since they have the SAME electron configuration.....BUT.....they dont have the same nuclear charge. As electrons are removed, the nucleus will exert a "pull " on the electron cloud........Here is an example.....We expect the Ca+2, with the greatest nuclear charge will have a greatest attraction of its electrons. S2- has the smallest nuclear charge will not have as much pull of its electrons toward the nucleus. Therefore, the ionic size: Ca+2 < K+ < Cl- < S2- (smallest) (largest) As you can see,,,,,,,just because they are isoelectronic does NOT mean they have the same size !!!!

Hope this helps.

Dr. Romano

Thank you but I guess my confusion was that I thought in order for something to be isoelectronic they all had to land on the same spot on the periodic table. In your example of "Ca+2 < K+ < Cl- < S2- " we see they all land on "Argon" . but in the book example only 2 land on the same spot and third one lands on a different noble gas (Al+++ lands on neon).

 

[DAT Destroyer]

Thank you but I guess my confusion was that I thought in order for something to be isoelectronic they all had to land on the same spot on the periodic table. In your example of "Ca+2 < K+ < Cl- < S2- " we see they all land on "Argon" . but in the book example only 2 land on the same spot and third one lands on a different noble gas (Al+++ lands on neon).

That point is moot. A specie with a +3 charge or +4 charge is VERY small.....and you should be comfortable enough to make an educated estimate on its relative size. Get a General Chemistry text, and look at the trends in atomic radius vs. charge. I think the Raymond Chang book shows it best. Hope this helps.

 

[Queen Beach]

This is an easy question and Dr. Romano explained it perfect!
This question is about atom size which you stated in the title.
All he said, was when a neutral atom gains e^- , the atom radii gets bigger bc you are adding e^-. However, the effective nuclear charge decreases which makes total sense... think about the middle part of a atom? It has protons(+). Does that make sense?
For Al+++, we took away e^- that's why it is smaller, therefore an increased nuclear charge. Protons>electons

 

[Mrhyde]

Thank you. I figured out a way for me to understand it better from all your comments

 

[DMikes]

lol but relating to what you said then you are contradicting yourself . When you compare Neon to Argon then that would mean Argon is larger then Neon since Argon lies below and thus is lower and size increases as you go down

There is nothing contradictory in my statement.

Argon IS larger than Neon. I'm not sure what you're talking about.

You don't even need to know anything about nuclear charge to answer this question. The periodic trends alone would've been sufficient.

Not only is Al3+ a +3 charged species, and thus very small, but it is an entire period above both K and Ca. That alone should tell you it is smaller than both. All that's left to compare is K+ and Ca++, which you seem to understand.


Perhaps I'm misinterpreting something?

 

[Mrhyde]

There is nothing contradictory in my statement.

Argon IS larger than Neon. I'm not sure what you're talking about.

You don't even need to know anything about nuclear charge to answer this question. The periodic trends alone would've been sufficient.

Not only is Al3+ a +3 charged species, and thus very small, but it is an entire period above both K and Ca. That alone should tell you it is smaller than both. All that's left to compare is K+ and Ca++, which you seem to understand.


Perhaps I'm misinterpreting something?

Nope your right, I was confused but I understand it now. The way I broke it down in my head was seeing that 2 were isoelectronic landing on Argon,so then I just use the isoelectronic rules for those 2 and then when I am done now I am left with Al+++ which would land on Neon. So then I think whats larger Argon or neon and argon is so thus Al+3 goes at the very last