I am having a hard time to imagine why does bond formation releases energy and where does that energy comes from?? It is easy to understand that breaking a bond requires energy because it can be viewed in many ways like breaking a wood into pieces requires energy, ripping your shirt into half requires energy, converting liquid water into gaseous water requires energy. These tangible concepts make it easy to understand why bond breaking requires energy. From these examples it answers the question why does bond breaking requires energy and where does that energy comes from (surroundings/thermal energy/mechanical force applied by the surroundings). But bond formation have so little comparisons and most of the examples associated with it are vague and hard to communicate with non science major. Thanks for the help.

  • $\begingroup$ Bond formation is like the same processes in reverse. True, this doesn't happen in our everyday world. Well, on atomic level it does. $\endgroup$ Aug 13 '20 at 23:24
  • $\begingroup$ Well, electrons have a lot of energy and can lose a bit. While why they lose it is hard to explain, the source is kinda simple. $\endgroup$
    – Mithoron
    Aug 14 '20 at 0:43
  • $\begingroup$ If you want to keep it simple, you can say that an electron (negative charge) that can interact with two nuclei (positive charges) has a lower energy than an electron near a single nucleus. Of course, this would mean that all atom-atom interactions would be covalent, which is not true. To understand this, you will need to get more sophisticated: orbitals, Pauli exclusion principle, exchange interaction... $\endgroup$
    – Rafael L
    Aug 14 '20 at 0:59
  • $\begingroup$ The shirt and the wood are not the best analogies. Two magnets are - take a look at Snatoms, youtube.com/watch?v=He30D8M5fNc $\endgroup$ Aug 14 '20 at 2:47
  • $\begingroup$ I think the shirt and the wood are good analogies because it is what ultimately felt at a macro scale. Just keep into account that some of the bonds might be not covalent. Nice question. Plus 1. $\endgroup$
    – Alchimista
    Aug 15 '20 at 22:10

It's a matter of perspective. You say you understand why bond breaking requires energy. In other words: $$\ce{A2 + energy -> 2A}$$

But consider the reverse reaction: $$\ce{2A -> A2 + energy}$$

This is also valid and can be understood in the following way: Bonds stabilize the electrons. In the unbound or atomic state, the electrons have a bit more energy. You can consider that atoms have some potential energy, like a ball on a hill. By forming a bond, the atoms "go down the hill" into a more stable state and thus lose this potential energy. This energy must go somewhere, and it is thus released in one form or another (heat, light, etc.) To break the bond is to push the atoms "up the hill" again, which requires energy.


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