size of atoms approximations

[PopeJoja]

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I have no idea how this even works. I read the explanation, but it hasn't sunk in for me yet.

Can someone explain how you deal with these questions?


Thanks!

here's the question on the free exam on gold standard.

[FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif]23) The CO32- anion is approximately the same size as:

1. Mg2+.
2. Ca2+.
3. Sr2+.
4. Ba2+.

It's C.


...

 

[PopeJoja]

also, how did you guys deals with phase diagrams?

 

[justhanging]

I have no idea how this even works. I read the explanation, but it hasn't sunk in for me yet.

Can someone explain how you deal with these questions?


Thanks!

here's the question on the free exam on gold standard.

[FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif]23) The CO32- anion is approximately the same size as:

1. Mg2+.
2. Ca2+.
3. Sr2+.
4. Ba2+.

It's C.


...

I remember doing this question, you have to infer it from the passage. It has something to do with the lattaice energy being greater if both the cation and anion were the same size then you go from there.

 

[PopeJoja]

Here's the explanation, though I still need help understanding it.

[FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif]SrCO3 is actually less soluble than the salt below it (see the table in the passage) despite the fact that Ba is situated lower down Group II in the periodic table. Thus the explanation given in the last paragraph has to be considered to explain the stability or extremely low solubility of SrCO3.

And they referred to this paragraph for the answer:

...[FONT=Verdana, Arial, Helvetica, sans-serif]However, there is one exception to these general rules. If the cation of the salt is approximately the same size as the anion, the arrangement of ions in the crystal lattice is more uniform and hence the lattice is more stable and ΔHlatt is more negative..

[FONT=Verdana, Arial, Helvetica, sans-serif].
[FONT=Verdana, Arial, Helvetica, sans-serif]
.

 

[justhanging]

Here's the explanation, though I still need help understanding it.

[FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif][FONT=Verdana, Arial, Helvetica, sans-serif]SrCO3 is actually less soluble than the salt below it (see the table in the passage) despite the fact that Ba is situated lower down Group II in the periodic table. Thus the explanation given in the last paragraph has to be considered to explain the stability or extremely low solubility of SrCO3.

And they referred to this paragraph for the answer:

...[FONT=Verdana, Arial, Helvetica, sans-serif]However, there is one exception to these general rules. If the cation of the salt is approximately the same size as the anion, the arrangement of ions in the crystal lattice is more uniform and hence the lattice is more stable and ΔHlatt is more negative..


[FONT=Verdana, Arial, Helvetica, sans-serif]
.

I can't explain it to you that well because I don't have the table or the passage. This is a passage question. The only thing I can say is that if something has a very negative lattice energy than they are not usually soluble because the bonds in the lattice are very favorable. Try to work of that.