My question is essentially about the factors that make certain atoms in certain compounds leave the compound they are currently in in order to bond with another atom/compound.

For example, I've been taught that if you react a halo-alkane with a strong base, like KOH, a substitution occurs in which OH and the halogen change places. Why does this happen (if it does)?

Would an electronegative atom rather want to bond with another extremely electronegative atom, or one that has extremely little electronegativity? Basically, would fluorine want another fluorine, or rather something like caesium?

$$\ce{Cs + F \to CsF}$$ $$\ce{F + F \to F2}$$

My thought is that fluorine 'loves' electrons so much, and there is nothing else that loves electrons more than this guy, so this has to be the most stable compound ever that is not dissociable by any other compound/atom.

  • $\begingroup$ There is a nice video about the reaction between cesium and fluorine: youtu.be/TLOFaWdPxB0 $\endgroup$ – SteffX Aug 14 '16 at 21:11

Any change which is spontaneous, takes place to lower the usable energy present in that system (This principle is so important, that even universe obeys it), which depends upon the conditions in which change in taking place. To demonstrate this, lets take an example of a stone at height h, one can do a lot of work with that configuration, it can do work by hitting someone on their head. But in contrast, when it is at ground, it does not do anything much on its own, the reason being it has used up some of its energy stored in the form of gravitational potential energy. Now of course, if conditions change, the stone can again do some work, in fact it is always loosing some of its usable energy energy, in the form of increasing entropy since it is breaking down by the natural forces of wind. Coming back to your question, why does substitution takes place in case of halo alkane with hydroxide anion. Now, we can see that haloalkane has transformed into an alcohol. If one calculates the usable energy (Gibbs free energy, this encompasses several other factors which include enthalpy, entropy and thermal energy) stored in haloalkane and corresponding alcohol, it will be clear that usable energy has decreased going from haloalkane to alcohol. To understand more about that, you can look up gibbs energy which quantifies that usable form of energy. Will fluorine bond with fluorine or Cesium- The answer, which I think is obvious to you, is surely cesium. why? Looking at their atoms, imagine cesium has no or very little pull on its valence electrons, while fluorine nucleus has so much pull, that electrostatic force permeates farther than atom. Hence, when two fluorine atoms come close to each other, there is some attraction between both atoms due to their individual pulls, but because both pulls are of same strength, it results in a covalent bond, but in case of cesium, the electrostatic force of fluorine nuclei pulls the valence electrons of cesium taking them away from the cesium nucleus, and thus fluorine's thirst for electrons is satisfied (the rock is at surface now!), while cesium is totally cool about it, since it had very little attraction for those electrons. After this process fluorine has negative and cesium has a positive charge, which attracts both of them and also it decreases the energy stored in fluorine-cesium systemIs CsF so stable that it cannot be dissociated into its components? No its not, put in water and water will dissociate the compound easily and energy is supplied by hydration and increasing entropy.

|improve this answer|||||
  • $\begingroup$ The first few lines of your answer are unfortunately either unrealistic explanations/interpretations that are sometimes purposely given to stupid kids (note that not all are thus) who will not be able to grasp the reality of the matter, OR very inaccurate examples. Universe does not obey rules, rules are our observations of how the universe works. Stone does not fall in order to reach a lower energy state, since it has no brain whatsoever to know that it will end up that way, rather, the reason it falls is because there is a reason making it do so (earth applying force on it), not, a purpose. $\endgroup$ – Emirhan G. Aug 14 '16 at 15:39
  • $\begingroup$ 2 questions: 1- Can I then infer that, the fluorine atoms in F2 would want to bond with atoms that are less electronegative than Fluorine? For example, if I had some fluorine gas and some pure carbon that doesn't have any crystal structure whatsoever (if possible), or, let's just say I have some phosphorus, will that fluorine gas react with those substances? 2- I believe, just as with the falling of the stone, when it comes to CsF dissociating in water, it doesn't do so out of a purpose, but rather, because of electrostatic forces (H2O is dipolar). So, would CsF dissolve in smt like C6H6 $\endgroup$ – Emirhan G. Aug 14 '16 at 15:54
  • $\begingroup$ In reply to questions, yes you can infer that fluorine atoms will choose to bond with less electronegative atoms in preference to fluorine atom since ionic bonds have lower energy state than covalently bonded compounds, for example if you mix chlorine atoms with Fluorine fluorine will bond with chlorine since bond formed will have some ionic character due to electronegativity differences , for reference, here is the link, where you can watch video of fluorine reaction with carbon (Charcoal).youtube.com/watch?v=TLOFaWdPxB0. $\endgroup$ – jaspreet Aug 14 '16 at 18:05
  • $\begingroup$ In response to your second question, no CsF will not dissociate in CsF, since there will be very little interaction with benzene, which will not overcome the lattice energy associated with CsF. $\endgroup$ – jaspreet Aug 14 '16 at 18:08
  • $\begingroup$ Regarding very first comment about so called unrealistic explanations. I am not sure, whether kids are provided with these explanations. This statement that every change takes place in the direction of decreasing free energy, can be thought of as a law, which helps to make sense, but in no way answers the why question. Just as newton's law of gravitation does make sense but in no why explains why. $\endgroup$ – jaspreet Aug 14 '16 at 18:15

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