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I want to know the intuition of why L is in the denominator of the equation for the energy of a particle in a box. This helps explain why resonance is stabilizing without using molecular orbitals. Does it have to do with the Uncertainty Principle? As the length increases, uncertainty of position increases, so uncertainty of momentum decreases, consequently meaning that the kinetic energy is lower, lowering the overall energy of the orbital?

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    $\begingroup$ It has to do with quantum mechanics. The uncertainty principle is not an axiom, but a derived statement. As such, it can't be said to "cause" things, but can be called to explain them. With that in mind, your reasoning looks right to me. $\endgroup$ – Ivan Neretin Sep 14 '20 at 9:01
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In quantum mechanics, particles are waves, and as with any wave the longer the wavelength the less energy is in the wave. You don't need the box to see this; infrared light has less energy in the photon than ultraviolet (the former makes you warm but the latter can damage your skin) and a slow moving free electron (lower energy) has a shorter associated wavelength than a fast-moving one (higher energy). In the particle/box problem, the possible wavelengths are set by the dimensions of the box; a bigger box allows longer wavelengths -> lower energies.

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