Just to add, I used an online calculator and the radius is 177 billion kilometers in diameter or 255 thousand earth's in diameter.

Agreed with the others in that it is somewhat arbitrary as in the is no fixed number and it may vary with the element or molecule in question. But we usually consider it when the aggregate of atoms is relatively stable and has bulk properties of the solid. A gas or clump of atoms even of the same type likely will not behave as a solid of the same constituents.

Well it's not the layman definition of temperature but, it is the actual definition 😉

I'll add since no one said this but gold does not oxidize. To get a metallic sheet so this and at this time it must be hammered thin. You can get gold so thin is transparent.

Being so thin the something made of really almost any other metal would be very oxidized.

Another difficulty is that most other metals work harden or are just much harder, for example platinum which does not oxidize well either does not forge into sheets like this easily.

So we are on the same page for the most part here.

But for the dissolution of salt you still have the bonds or really lattice energy to overcome. The totally enthalpy is negative as you make most of the energy required to break the bond during solvation but it still requires that energy, i.e. it's endothermic. This is what I alluded to in the multiple reactions. Total enthalpy is the sum of the bond/ lattice energy + the sum of solvent-solvent attraction energy - the sum of the solute- solvent energy.

Maybe I'm missing something but you still use the standard bond enthalpy for this equation. I.e. the sum of all the reactions enthalpy. Curious on your thoughts here.

Edit: I will agree that bond strength is not especially representative to the common environments like aqueous one.

One thing I would point out is that the difference in energies between the start and end states are the same no matter the situation. The the examples you give are where the bonds can more easily be broken because the intermediate states are more easily reached. I.e. before the O2 is separated out most first have the bonds Bricker and both O2 would be so reactive that in the time they are separate they would just bond back to one another. This requires a lot of energy i.e. to make something catch fire you need to first provide enough energy to do this, usually with something very hot. In our bodies the intermediate state where they are not bound or loosely bound is stabilized by specific molecules in our body making it easier to break the bond in O2. Since this intermediate state is stabilized you don't need the large initial energy to initiate the reaction (some energy is still needed). However, the energy produced is still the same as it depends on the final and initial states only. Edit: while this is true often there is more than one reaction happening such as enthalpy of solvation, solvent- solvent integrations, and solvent solute interactions.

That said the bond energy of NaCl is 787 kj/Mol and O2 is 498 kj/mol.

Is point out as well your teacher is not correct. Ionic bonds are stronger. But, in an aqueous state they can much more easily be solvated due to water stabilizing the intermediates. Ionic bonds since they do not share electrons, once separated are very easily stabilized. In covalent bonds this is generally not the case.