-1
$\begingroup$

When we consider the alkaline metals for example, we say that an atom of a metal like sodium gains stability by losing an electron, however this doesn't seem to be a very meaningful statement. Either it should be like it gains stability and finds a lone electron to be a hindrance in being stable and thus loses it. Even then, on losing the electron, it gains a positive charge and thus become unstable in just another way. So how does the mechanism of attaining stability exactly work? How does a species know that some act or process is going to give it stability? Since it doesn't know this how does stability reach it?

Further, what exactly does it mean to be in chemical stability by losing/gaining/sharing electrons, forming ions/bonds[of various forms] or by changing chemical partners etc.? What is their purpose exactly? Is it to have the least energy possible? And why is it that some things are more stable than the others from the start[not the very start possibly]?

I wanted a notion of stability + the mechanism to get it and retain it. [in simpler words that one would likely use for addressing high school science students, please]

$\endgroup$
5
  • 1
    $\begingroup$ The first point is that Na loosing an electron does not become more stable. It can be if another species is involved. It happens many times that sentences take their status in a truncated form. (Similar to E = mc2 :)) $\endgroup$
    – Alchimista
    May 17 at 10:52
  • 7
    $\begingroup$ Stability is much like patriotism. Whoever talks about it is most probably trying to fool you. $\endgroup$ May 17 at 10:58
  • $\begingroup$ The enthalpy of formation of $\ce{Na}$ is $\pu{0 kJ/mol}$. The enthalpy of formation of the ion $\ce{Na+}$ is $\pu{-240 kJ/mol}$. So the ion $\ce{Na+}$ is much more stable than the neutral atom. $\endgroup$
    – Maurice
    May 17 at 11:27
  • 3
    $\begingroup$ @Maurice Formation enthalpies of ions are placed on an entirely different scale with $\Delta H_\mathrm{f}(\ce{H+}) = 0$ by definition, see e.g. Atkins et al. Physical Chemistry. It is not right to compare the two numbers you have compared. $\endgroup$
    – orthocresol
    May 17 at 13:38
  • $\begingroup$ @orthicresol Hf of Na as equal to zero is even that of a piece of metal. I don't know how that comment came up. $\endgroup$
    – Alchimista
    May 18 at 9:07
4
$\begingroup$

Dear Lumbini A Tambat:

Thank you for pointing out one of the simple concepts that get overlooked in teaching. Teaching chemistry especially! Stability. With reference to what? It's easy to imagine so many ways to get un-stable, but how can you get more stable, if you are an atom?

Well, darn it, a sodium atom is quite stable, all by itself. You can shake it, heat it, freeze it, bang it (within limits), and it remains quite unchanged. Sodium metal at 0 $^o$C and 1 atmosphere pressure is in its ground state, as stable as it can get because there is no state more stable. This is Standard Temperature and Pressure. (https://www.thoughtco.com/difference-between-standard-conditions-state-607534) Of course, we have to complicate it a bit, so we also have Normal Temperature and Pressure (NIST uses 20$^o$C), and there are 21 different modifications of the exact temperature and pressure that constitute a standard or normal temperature and pressure. https://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

But the point is that there is some generally well-defined set of conditions under which we classify materials as being in the lowest energy state possible, or most stable, or in a ground state, from which we do all our calculations and reactions.

It is possible to take two materials, both in their respective (lowest energy) ground states and allow them to react to form a new material which is now more stable because it has released some amount of energy - if you consider the two original materials, e.g., sodium and chlorine, to be in their ground states, imagine that the energy released digs a hole to an even lower ground state. That lower energy state exists because Na$^+$ ions are strongly attracted to Cl$^-$ ions in a sodium chloride lattice, and that energy of stabilization was enough to knock an electron off a sodium atom and force it onto a chlorine molecule, splitting it into pieces, one of which become a chlorine anion.

Now we explain the final situation as having a stable sodium cation, so it must have stabilized (because it can't get changed any more under ordinary chemical reactions). So now it's really stable. Unchangeable. Well, you could dissolve it in water and hydrate it, and it could become a little more stable, but not much. And the chlorine atom has an extra electron and seems quite stable: it doesn't explode or anything. But were you looking when the sodium and chlorine were reacting? They didn't look at all like they were getting stable - it would have been quite exciting!

enter image description here

http://derekcarrsavvy-chemist.blogspot.com/2016/12/lattice-energy-1-calculating-lattice.html

In the picture, NaCl is the lowest energy material. The sodium is "stabilized" by the chlorine. This level is the ground state for NaCl. The next line above is a ground state for two elements, sodium and chlorine. They are stable in themselves, if kept separate, but they have reactivity, which also conveys the idea of instability. So which is it? Stable or unstable? This is where the teaching function often breaks down: one word means two entirely different things, yet we manage to communicate successfully - if we have been forewarned. We still sometimes trip ourselves up.

In the picture, we start with stable Na (solid), put in energy to vaporize it to Na (gas), put in more energy to ionize it to Na$^+$ plus an electron, then shift to the chlorine, dissociate it to atoms by putting in energy, then let a chlorine grab the electron (giving off some energy), then allowing the sodium ion to condense with the chlorine ion to form a lattice of NaCl and give off the lattice energy, which makes the final product (NaCl) so very stable the we have tons of it in the sea and in salt mines all over the earth.

Now if you have a supernova available, you could turn the sodium into iron, which is really the lowest energy you can get to, but in most labs, the diagram illustrates several levels of energy, and conditions where the materials are stable, but could react to form something more stable. Sodium is reactive and stable at the same time, depending on the conditions.

$\endgroup$
3
  • $\begingroup$ This might turn to be useful many times. $\endgroup$
    – Alchimista
    May 17 at 13:48
  • 1
    $\begingroup$ hal.archives-ouvertes.fr/hal-00516229/document is an interesting reading. The misconceptions are so widespread that it is difficult not to blame school and teachers. $\endgroup$
    – Alchimista
    May 17 at 13:53
  • $\begingroup$ @Alchemista: Very interesting link (43 pp!). I suspect that is why lab work is so important. And demonstrations of effects that are not suitable for individuals in the lab so as to illustrate some examples with real, visible material, not just a chart or diagram. I was captivated in freshman college chem course by a demonstration of acetone vapor pressure in a mercury barometer: more acetone did not give more depression of the Hg column! How could that be??? Even more memorable than the H2 +O2 soap bubbles exploding best at a 2:1 ratio. $\endgroup$ May 17 at 19:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.