Why do reactions happen at all? [closed]








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What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and Chlorine, it seems intutive to have number of combinations from this pair such as $\ce{Na2Cl}$, $\ce{NaCl2}$, $\ce{Na3Cl2}$, and even do not react at all. But why $\ce{NaCl}$?


I had been carrying the concept of octet rule, which I now find to be exception in some cases like $\ce{AlCl3}$. So, what determines the products of a reaction? Or is it that all possible combination are formed but only few are major products, in this case $\ce{Na2Cl}$, $\ce{NaCl2}$ etc. are formed but $\ce{NaCl}$ is major product.


I think it has to do something with energy but cannot figure out what.





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> What makes some atoms/compounds reactive and some noble?
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Unpaired electrons and how tightly these electrons are bound to their respective nuclei.



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> Why do reactions happen at all? What is the fundamental truth behind a reaction? 
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[![enter image description here](https://i.stack.imgur.com/eUKG2.gif)](https://i.stack.imgur.com/eUKG2.gif)


Because atoms are more stable together than they are apart, and systems will tend towards their lowest energy state.



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> But why NaCl?
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This is really a matter of ratios, which is the basis of chemistry. Different elements share their electrons in different ways under different circumstances. Some can donate their electrons ($\ce{Na}$, $\ce{Al}$, $\ce{Au}$), some accept electrons ($\ce{Cl}$, $\ce{O}$, $\ce{N}$), and others are somewhere in between ($\ce{C}$, etc.). Sodium and chlorine are very consistent with how they share electrons. Sodium has 1 valence electron, chlorine lacks 1 valence electron, and they combine in a one-to-one ratio. The formula unit of their salt is $\ce{NaCl}$.


When considering the salt of aluminum and chlorine, ask how many valence electrons does each atom have/need. I think you might begin to see the pattern.




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$[1]$ [Bond energy diagram](https://www.sparknotes.com/chemistry/bonding/ionic/section1/)


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